Peter Crouch.A Career Projection.

The continued ability of the English Premier league to attract talent has proved to be a double edged sword for some of the second tier members of England's top tier.Whilst on the one hand any precocious talent who bursts onto the world stage at a top international tournament can be expected to land in England and torment defences sooner rather than later,there is also the opportunity for lesser teams to purchase talented,but ageing stars who suddenly find themselves surplus to requirements.The likes of Fowler,Wright and Owen turning out for Manchester City,West Ham United and Newcastle respectively was just a precursor for the likes of Stoke,Wigan and Birmingham to be able to attract proven goalscorers to their less fashionable homes.

Predicting an ageing pattern for sportsmen as a group is probably one of the most problematic conundrums possible.What seems like a deceptively easy task is actually one that is riddled with pitfalls and selective bias.For example if you want to see how many games on average a 29 year old plays over a season,you can not simply take the record of all players of that age and average the total.The group of 29 year olds is actually a selectively biased sample of players who actually played games during those years.Some 28 year olds may not have played at all during their 29th year,either because they weren't good enough to command a start or perhaps because they were long term injured.So if you are a manager eager to snap up a bargain older player,simply looking at how 29 year olds performed on average will almost always give you an inflated and over optimistic view of how your purchase might perform.

It also seems likely that player position can be an influence on a player's expected decline.Goalkeepers especially managing to achieve to acceptable levels of performance much later in life than the more physical roles played by outfielders.

Of particular interest to Stoke City fans is the question of how the record signing of Peter Crouch will pan out over the anticipated four year duration of his contract.Crouch is a member of a select band of strikers who have scored 100 EPL goals,a testament to both longevity and scoring prowess.So I propose to see how the career profile taken by this select group of players has ebbed and flowed,paying particular attention to the likely amount of games these players can play as they age,how their goals per game ratio changes and how Crouch's career numbers fit into these projections.

Peter Crouch,a member of the 100 EPL goals club.

Around 20 players have reached the 100 EPL goals milestone and around half of these players have effectively retired from actively playing top flight football.If we begin by looking at just these retired players,we only have to account for players who are absent from the sample due to dropping out of the top flight and not those who are absent from the older age bands because they are too young.Also as most of the players in this group played the bulk of their games in the early years of the Premiership it might allow us to compare the state of the EPL now to how it was then,for top notch strikers at least.

If we start with appearances.Our sample makeup is biased because we are looking at how players who we know were destined to score at least 100 EPL goals fared in their early years.We hope to mitigate that sample bias by looking at a very narrow band of conclusions,namely how 100 goal players age.We are simply trying to second guess the viability of purchasing proven goalscorers who are in all probability past their best. Therefore,in this initial group of retired players we simply have to account for the players that weren't in the early years and those that drop out of the sample in the later ones.I'll do that by assuming that all players are always present or remain in the group,but if they are no longer playing in the EPL then they contribute zero games for each age they are absent.This process is artificial in the early years because from the limited data we don't know which players will achieve great scoring feats.

These problems also exist in the group of players who are still active in the EPL,but additionally younger players,such as Rooney are not present in the older age groups for the obvious reason.All I propose to do at the moment is to exclude the younger players from the sample beyond their current age and hope that the current batch of older players are reasonably typical of those who will follow.....I did say ageing studies were problematical.

The two subgroups of goalscorers contain around 10 players each,so for an age related season where each striker could play a maximum of 38 games there are 380 potential games available for that age of generational player.If the cumulative total of games played by all the eligible players was say 280,then I've plotted that age band as taking part in 74% of the total available games.

Percentage of Playing Time Seen by Players with 100 or more EPL Goals.

 By plotting the average percentage of total available playing time actually played by each group,we can see that current strikers were either asked to or were able to play a higher proportion of league games compared to their earlier counterparts.The sample sizes are small due to the restrictive parameters we've used and the methodology becomes more ad hoc as we see the likes of Rooney dropping out of the batch of current players.But there seems a definite trend for the current top class striker to play more often,younger and this generational gap then starts to narrow at around 28 years of age.Whether current scorers longevity will then dip below the trendline for the previous generation can only be speculated upon,but the current player may well be seen more often earlier and slightly less so later.

Today's 100 goal players,it could be argued are more multi dimensional than previous out and out goalscorers,but a manager seeking to grab an expensive addition to his strike force today will still be expecting goals to be part of the package.We've seen in previous posts that scoring rates can be deceptive,20 goals from 30 games is the same scoring rate as 2 goals from 3 games,but as a seasonal output the former is much preferable to the latter.So when we move on to goal output I've calculated a seasonal rate instead of a rate tied just to actual games played.Potentially players can play 38 EPL league games,so I've used that figure whether they played all 38 or not.When deciding to purchase a player one of the overriding concerns should be how many goals will he add to my teams seasonal total and this approach measures how the pool of players from which we are making our purchase have performed in this respect over time.

Seasonal Goal Rates for EPL Players with 100 or more Goals.

We saw in the appearances graph that the later generation of EPL scorers were seen more frequently,earlier in their careers than had been the case for the earlier generation.So it's not surprising to see the former out scoring their elders,albeit with the gap closing.The current crop of strikers do appear to then be outscored on a seasonal basis by the old guard,however the group does not include any numbers that Rooney may put up post his 27th birthday.So while the trend should be noted,the conclusions are far from being set in stone,Wayne will probably push the green line much closer to the red one once his more mature years are added to the mix..

So how do these graphs relate to what we know about Peter Crouch.

In terms of playing time he appears to be a slight throwback to an earlier generation.Mainly through lack of opportunity he was only playing around 40% of the available top flight games he could have played in his early twenties.So when the currently playing crop of  goalscorers are starting to see their playing time decrease at around about 26,Crouch was actually still on an upward curve and he only started to see opportunities decline as he passed 28.Encouragingly he was still capable of playing almost 80% of the available EPL league games when he reached 30.The benchmark figure for top strikers in their 30's is around 75% of league appearances,so Crouch is slightly ahead of the ageing curve but not freakishly so.By 34 when Crouch's current contract expires a typical prolific and long lasting goalscorer was on average still appearing in just over half of his team's league games and,barring catastrophic injury Crouch would expect to do at least as well as this.So 30 plus games in the first year of his contract,dropping to the low 20's by the end seems a realistic estimate for Crouch to achieve,but we really want to know how many goals he'll contribute to Stoke if they continue to invest throughout the side and stay a Premiership side.

This final graph is Crouch seasonal totals expressed in terms of goals per maximum possible number of league games that he could have actually played (this convoluted approach is necessary to account for the occasional 42 game season).A single player sample is going to be more noisy than a larger sample size,but Crouch's goals per 38 game season has been between 0.2 and 0.25 goals per game for all of his later years.These numbers make him a legitimate member of either the Shearer led older group or the Wayneless present collective.

The best case scenario for Stoke fans is that their £11 million record signing has in his dotage the resilience and scoring rate of the earlier group,coupled with the added extras that enables the more recent group to keep being selected despite an apparent decline in scoring ability.In raw goalscoring terms he could reasonably expect to be scoring 12 goals in his first season,falling to around 8 in his final year.Perfectly acceptable returns for a team whose top scorer rarely breaches double figures.

Goals Scoring Profiles for the EPL's Most Prolific Scorers.

In this post here I looked at the goalscoring profiles of the most prolific strikers who had combined lethal finishing with a longevity of career to amass 100 or more Premiership goals.The piece concentrated on the ongoing career of Thiery Henry who is currently back at Arsenal on loan from he MLS,but the career statistics of the rest of the 100 club were also collected and it seems a shame not to publish those as well.

Goals scored per game does a good enough job at rating a goals scorers ability,however it does tend to favour players who were on teams which scored lots of goals.Therefore I usually express a goalscorer's core statistic in terms of his goals per game rate as a proportion of his team's goals per game rate as this gives a little more context around the kind of goal scoring environment the players was performing in.It also helps to highlight how integral a player was to the team's overall goal grabbing ability.For example if  player scores on average a goal a game for a team which scores on average 2 goals a game,his scoring rate is half that of his team.If his team scores 3 goals a game,his rate is only a third.


Alan Shearer.


We'll start with the archetypal English goalscorer,Alan Shearer.Shearer started his career with top flight side Southampton in the old First Division,before moving to cash rich Blackburn at the inauguration of the Premier league and finally seeing out his time at Newcastle.

Shearer's career peaked between the ages of 22 and 26,encompassing his last three seasons at Blackburn and his first season at Newcastle,when his goalscoring rate was almost half that of his team as a whole.His scoring rate then declines compared to that of his team in fairly typical fashion for elite goalscorers as a group.There is a noticeable dip in 1997/98 when an ankle ligament injury restricted his appearances to less than half a season.Even allowing for his limited game time,his goalscoring rate during that season was barely one tenth of the team's indicating that he was ineffective even when he did manage to play.He retired from international football in 2000,but suffered another,less dramatic injury hit season,but remarkably and definitely atypically for elite goalscorers he produced a season that was comparable to his best in his 33rd year,a feat made even more remarkable for his near perfect appearance record.This Indian summer is reflected in the upturn in Shearer's graphical profile just prior to his retirement.


Michael Owen.

Another Newcastle player,Michael Owen of course is best remembered for his time at Liverpool.He is often cited as a player who played his very best football in is early twenties and whist it's true that he did produce extremely impressive number over that time scale,he does manage to peak only a year sooner than Shearer.Owen played in Liverpool sides with a multitude of goal threats,he overlapped with Robbie Fowler another 100 EPL goals man,so Liverpool were never as reliant on his goals as Blackburn and Newcastle were on Shearer's.Never the less Owen's achievement of averaging over 30% of his consistently successful side's scoring rate during the first seven seasons of his career was mighty.His fall,however has been precipitous as injury has blighted his appearances and his eye for goal.A metatarsal injury at Tottenham in his first year at Newcastle heralding the start of Owen's decline.

A rare sighting of Michael Owen on a football pitch.

Wayne Rooney.

The first graph for an elite scorer who is still playing regularly and is still somewhere near to his peak.Rooney's plot tells us both something about the nature of team goalscoring in the most recent past and something  about Rooney's increasing importance to Manchester United.Rooney's teams have spread the goalscoring around and his scoring rate of around 30% of a team replete with the likes of Ronaldo and to a lesser degree Berbatov is just as impressive as was Shearer's 50% rate in a less goal hungry outfit.Rooney is already older than both Owen and Shearer were at their peak and his increasing contribution to a continuously successful United team shows why Sir Alex didn't chose to go down the Beckham route following the recent unrest between himself and his premier striker.


Robbie Keane.





Another refugee from the MLS,Keane shows the classic ageing profile for strikers.The plot does not account for appearances,therefore the steady decline in scoring rate compared to that of the teams he was playing for is more likely to be down to a slowing reflexes rather than lack of opportunity.If anything Keane's decline has been the most dramatic of the players still active in the EPL,his team corrected scoring rate has reached the level a typical elite striker on average reaches in his mid to late thirties,not his early thirties.Keane's regression possibly explains why he chose to decamp to a lesser league rather than try to secure a permanent deal with another EPL team.His brace against Wolves on his loan return we'll chalk down to fate.


Robbie Fowler.





Probably the most precocious of the scoring talents of recent years.It's usually more difficult to hold your own in terms of scoring rates in a successful team,but that's what Fowler managed to do from the very start of his career.He was scoring goals at 40% of the rate of his Liverpool team when just out of is teens.His career didn't peak,it just started high and steadily declined to age related rates that were below those generally seen in player in their mid twenties.To his credit he hauled his pre retirement numbers up towards nearly average levels during a swansong back at Liverpool. 


Ian Wright.

A relatively late starter to top flight football,Wright was almost 22 when he first played league football for Crystal Palace in the second tier.It was four years before he helped Palace make the step up via the playoffs and possibly because of his later start he saw his career peak with Arsenal a year or two later than the average.As a twenty nine year old he was banging in goals at a rate that was over half that of his team and even as a 35 year old he was scoring at rates that wouldn't have looked out of place in an average,elite scorer who was still around his peak.He also managed a double figure goals tally in his final year in the lower leagues,despite turning out for three different clubs.


The above graphs just give a flavour of each player's career,for instance scoring rates can be misleading where no account is taken of appearances made.A player scoring two goals in a single season appearance will have a very impressive scoring rate,but a team is likely to prefer a player who has a less impressive goals per game ratio and a larger number of games played.Fortunately,most of the above players have had prolonged stretches where they have played consistently.However,in the next post we'll see how often the very best goalscorers have been able to make it onto the pitch as they progress through their careers and we'll try to see if buying a proven,but ageing goalscorer such as Peter Crouch can be a good deal.

Home Advantage and Personal Duels in the EPL.

One of the most enduring and enigmatic features of modern day sport and football in particular is the existence of home advantage.Although the scale of a football team's home field has been declining fairly steadily over the course of the last and present century it is still a major factor in the sport.It's very common for individual teams to apparently buck the trend of teams performing better on their home turf,but these instances are always as a result of small,single season sample sizes and when measured over longer periods virtually every EPL side shows a preference for their home venue.Home teams have goal differences that are around 0.8 of a goal inferior on the road compared to at home and home success rates hover just below 60% at home compared to just over 40% when they're away.

We discussed and quantified home advantage in the EPL here and suggested a partial contributor to the effect here,in this post we'll try to use some of the more granular stats that are being made available and match these numbers to some of the more innovative research that has been done in the field.

Many factors have been proposed as playing a role in setting home field and whilst some have been discounted,others certainly play a partial role.Travel effects have in all probability declined with the improved transport network and over night stays becoming the norm.Crowd influence is probably an overstated factor.A research paper indicating that referees give different decisions when shown footballing incidents with the absence and presence of crowd noise was conducted with amateur refs from Staffordshire.From personal experience,not the most reliable of control groups.Familiarity with the playing surface is also probably less of a factor in football where there is little scope for improvisation in the presentation of the pitch.Very few professional grounds have the pronounced slopes that were part of the folk lore of giant killers such as Yeovil.Derby have long since departed from their quagmire at the Baseball Ground and present day Stoke with their narrow Highburyesque pitch are the closest you'll find to a team/pitch combination tailored to the needs of the hosts.

A more novel approach to home advantage appeared in the early 2000's when researches found an increased level of natural testosterone in both soccer and ice hockey players prior to home games compared to away contests and none competitive games.These increased levels in theory could lead to elevated aggression,better endurance and reaction time and additionally an enhancement of the passive aggressive effect postulated by evolutionary biologists when "trespassers" meet adversaries on none neutral ground.

Is seems reasonable to assume that if this phenomena is widespread in professional sport it will show up in the results of the many dozens of individual battles that occur during the duration of a team sport.Opta via it's resellers such as EPLIndex and the Guardian Chalkboards are gradually making more detailed statistics available and although the integrity  and accuracy of these numbers is inevitably going to be slightly suspect through different interpretations of similar events by different data collectors,coupled with the mammoth task of maintaining massive databases it does open up new lines for investigation.

The success rates for individual tackles and the results of individual duels between players could be the kind of footballing incidents that are effected by the venue specific swings in both testosterone levels and heightened aggression.Therefore,I recorded how successful teams were in individual game incidents when they instigated tackles or duels at home and then on the road.

I chose the 2008/09 season at random and plotted how the percentage success rates for the cumulative individual totals for all 20 teams from that season changed for home and away games.Before we look at the graphs it's worth noting that one season is not sufficient to fully capture even such a fundamental feature as home advantage beyond doubt.The overall home and away trend should be evident,but there will be random outliers due to the relatively small sample size and so we should expect similar variation when looking at tackle or duelling events.

How a Team's Success Rate in Ground Duels Varied by Venue in 2008/09.

The best correlation from the three categories of on field,individual challenges that I looked at was for one player taking on an opponent on the ground.It's hard to imagine a contest more suited to demonstrating the presence of an elevated state of endurance,aggression and reaction time than this type of challenge.If the testosterone study has validity we are likely to see accumulated team success rates in these type of situations generally decline on the road and on the limited evidence of one EPL season that is what appears to happen.Based on the regression line,a team which wins 50% of these type of challenges at home would likely win just over 49% of them on the road.

A Naturally Aggressive Home Player Wins this Ground Duel with two Passive Away Opponents. 

How a Team's Success Rate in Aerial Duels Varied by Venue in 2008/09.

A similarly strong correlation exists for aerial battles.For much the majority of the line of best fit where the bulk of the points lie,teams win a higher proportion of aerial battles at home than they do away from their home stadium.The situation is briefly reversed when we look at the few very worst of performers,this may be a quirk of less robust sides or it may disappear in larger sized samples.

How a Team's Success Rate in Tackles Made Varied by Venue in 2008/09.

Possibly the most interesting set of results comes from the success rates of tackles made on opponents.There seems at first glance no reason why the percentage of successful tackles made by teams should not also benefit from the increased testosterone fuelled,none passive approach that prevails at home.Yet we see the reverse for almost half of the trendline.Teams actually appear to complete a higher proportion of tackles away from home than they do at home at lower completion rates.However,a team making 78% of successful tackles at home are only predicted to complete 76% on their travels which is more in keeping with the trends seen in duels.

A clue may be found in Opta's definition of a tackle.A tackle is deemed a success if it is played out of play and is "safe".If home teams are leading as they more often are at home,particularly late in the game they are also quite happy to see the ball out of play and safe,especially as they still retain possess from the throw or kick.This allows the away side to notch up artificially higher tackle counts with the complicit agreement of the home side.There's not quite the same level of guaranteed benefit to the (leading) home side in allowing the visitors to win a ground or air duel.Tackles are like shots on goal much more hostages to game context and a rich subject for further,more detailed investigation.

So far we've shown that duels if not tackles are won more often by the naturally pumped home side,but before we can reasonably conclude that these numerous individual pitch battles accumulate and contribute to home advantage we need to see if ground or aerial success rates are correlated to overall team success rate in games played.

 How a Team's Seasonal Success Rate in Matches Correlates to it's Seasonal Success Rate in Ground Duels.

As before the trend and direction of the line of best fit is of more interest than the relatively weak,sample size driven correlation.The results are pooled from both home and away matches this time because we are simply interested in if winning a higher proportion of your ground duels enhances your chances of winning the game.And the upward direction of the slope indicates that this appears to be the case.A similar graph results from the data for aerial duels.

So to conclude.Various limited studies seem to indicate that home teams have elevated,naturally occurring testosterone levels compared to when they are the visitors and evolutionary biology suggests that species have evolved to act more aggressively when on their own turf.These two interconnected facts appear to be confirmed by home teams winning higher proportions of individual duels during matches and winning more of these duels correlates with winning matches.And this may go part of the way to explaining the universal occurrence of home field advantage in football.

Thanks to EPLIndex for access to the stats used here.