Pages

Tuesday, 5 June 2012

Do Interceptions Matter to Teams ?

In terms of excitement and importance to the overall outcome of the contest,rugby of both codes and the NFL have cornered the market in interceptions.An interception is a relatively rare event in both sports,but it can be a game changing one.In a field position based sport such as the NFL the event always costs the transgressor points,both in the potential points lost by their offense and potential points handed to their opponent's offense as a result of the turnover.Similarly in rugby,the interception is relatively rare,but because the majority of the players will be stretched across the pitch close to the incident,it gives the intercepting team an excellent opportunity to at worst make considerable gains in territory and quite often it also leads to an unopposed score.

By contrast an interception in football is much more low key.It doesn't have the rarity value and unless a team can intercept an opponent deep in their own territory,it rarely produces anything dramatic or game changing.Admittedly,it's unlikely that Ebbsfleet's keeper,Preston Edwards would have ever been sent off just 10 seconds into a game,without ever touching the ball had it not been for an intercepted backpass and Stuart Pearce and San Marino would not be inextricably linked in World Cup history,but these types of interceptions are rare and uncommon.In truth most football interceptions pass virtually unnoticed.In a game where changes of possession is commonplace,they are simply another way of losing the ball.Sometimes the interceptor will receive a brief round of applause and sometimes the player getting intercepted will get the same for showing adventure and ambition.

Team and individual player interceptions are now readily available from such sites as EPLIndex,but the usefulness of these newly available statistics is still unclear.As with all counting stats they do an excellent job of recording on field events,but often their value can be obscured because they are often presented without context or connection to a team's success or failure.

How you use numbers such as interceptions is at the heart of the new wave of statistical analysis of football.Unlike set piece sports such as baseball and territory based sports such as American Football and to a lesser degree rugby,football has a much more diverse tactical approach.To take an obvious example,often soccer teams will go backwards to regroup,whereas except in particular endgame situations this is never the case in the NFL.Therefore,how football teams accumulate secondary counting stats such as interceptions can depend greatly on both match situation and their tactical approach.

If we take the example of three teams from 2011/12 who enjoyed varying degrees of success.Manchester City,Champions of course,as a team made 648 interceptions over the season,Stoke who just about finished midtable had 497 and Aston Villa,who lost their manager but held on to their Premiership status recorded 786 interceptions.

Interception Rates for Three Teams from the EPL,2011/12.

Team. Passes Attempted by Opponents. Interceptions
Made by Team.
% of Passes
Intercepted.
Manchester City. 14524 648 4.5
Stoke City. 17115 497 2.9
Aston Villa. 17078 786 4.6

There's no obvious correlation between these three raw interception numbers and overall finishing position.So the first step is to try to introduce some type of context.Where the interceptions occurred and what the score was at the time would be a marvelous addition,but it will unfortunately have to wait for much more detailed figures.However,to effect an intervention you need your opponent to pass the ball,so at the very least we can change interceptions to a rate figure.Stoke and Villa's opponents each attempted 17,000 passes over the season against the two Midland teams,while Manchester City's opponents tried just 14,500.So we can start to add more context and more value to these raw counting stats.Both Villa and Manchester City intercepted around 4.5% of their opponents passes,while Stoke intervened on less than 3% of occasions.

The Relatively Rare Sight of a Stoke Player Attempting an Interception.

Next we need to try to deduce the on field distribution for these events.It appears that just under half of a team's interceptions are made by defenders,the vast majority of the rest are made by midfielders and less than 10% are made by strikers.This makes intuitive sense.When defenders are playing the ball out of defence they have more space and they really don't want to give possession away,but when strikers and midfielders are playing passes deep in an opponents half,the downside of an intercepted pass is merely a lost opportunity with little immediate threat to their own goal.Therefore we can speculate that interceptions are predominately made in a defensive context.

We can now look at a game level to see if an increased rate of interceptions,primarily we speculate in a defensive situation can help a team to achieve a favourable result.I've used avoiding defeat as the definition of an acceptable outcome and I've also required that the connection between more efficient interceptions and a good result is unlikely to have appeared by chance.

In the case of Manchester City there is no connection between improving rates of intervention and improving results.Such was City's superiority last season,they could have conceded an extra goal in over half of their games and still won the match,so even if being better at intercepting passes makes more likely to win,it seems likely that in City's case this possibly defensive effect would be overwhelmed by their attacking prowess.

By contrast Villa and Stoke were the two least potent attacks in the EPL,so if a talent to intercept helps a defense then we should be able to see a game by game correlation between efficient interception rates and results.Both teams conceded about as many goals as did teams who finished around 10th in the league and they bettered the goals against totals of half a dozen teams.So their relative success was based around a reasonable defensive showing rather than the dazzling attacking intent of Manchester City.

In contrast to the Champions,Villa show a very strong correlation between interception rates and success on the field.Their chances of taking at least a point from the game increases with increasing interception efficiency.Based on a regression of last years results,they had around a 30% of taking points from the game when they intercepted 3% of their opponents passes,but this figure jumped to a 90% chance of points if they intercepted at a rate of 8%.Of course correlation does not imply causation,teams may be attempting more adventurous passes when they are either stalemated with or trailing to a poor Villa side and Villa may be building up their interception rates after they have gained control of the scoreboard.Viewing Villa's 2011/12 games with an eye to this information should enable anyone to decide if aggressively chasing interceptions was a key factor in Villa achieving their limited success last season or whether it was a mere by product of a favourable game situation.All this may be moot next term with their change of management.

Stoke by contrast had virtually identical defensive statistics as Villa did last term,but very different interception rates.Not only did The Potters intervene at a much lower rate,only 3% of opponents passes were picked off compared to 4.6% for Villa,but there was no correlation between that rate and success on a game by game level.It would seem that interceptions play no part in Stoke's matchday game plan and defensively they are much more about team pressing to force mistakes or speculative shots from distance.The risk reward of going for a pick it would seem is too much for the ultra cautious Tony Pulis.

We've started with a raw stat that many consider of very little value and hopefully we've turned it into a slightly more useful figure that may indicate how some teams set up their defence.Any information is welcome and better than none at all,but potential gains can be made by simple manipulation of the figures.The sample of teams has been necessarily small because data has been require on a game by game basis,but we have been able to speculate that interceptions may have played a fairly significant part in the way Villa's defence performed under Mcleish.It was his attack that underperformed from the previous campaign and ultimately sealed his fate.

There is decent evidence from the NFL that shows that an ability to intercept the ball is a repeatable skill and while the current counting figure for individual players in association football are welcome,they do fall way short of those available on a team level.For example we can barely speculate on the value of large number of interceptions by a single player because we don't even know how many tempting passes have been played towards him.So if teams are being built to pick their opponents pockets,they presumably are using video analysis as a bare minimum to recruit their squad additions.

Interceptions may be lower in the pecking order of more advanced stats than other more universally predictive figures,but there is some reason to suggest that they do illuminate the bigger team picture some of the time.

Sunday, 3 June 2012

How the Composition of the EPL has Changed Over 20 Seasons.

One of the benefits of the massive amounts of money that has poured into the English Premiership since it's inception has been the subsequent ability of teams to purchase the best talent from around the globe.The following graphs chart the changing make up of the origins of the talent over the league as a whole through 20 seasons.

Initially the majority of the non English talent in the EPL unsurprisingly came from the three other home countries of Scotland,Wales,Northern Ireland as well as the Republic of Ireland.Numerically the amount of players from these four near neighbours has remained fairly constant over the twenty seasons,However proportionally their influence has steadily declined as teams have purchased initially from Europe,but latterly from the Rest of the World as well.The biggest fall has been seen in the number of English born players making at least one start per season in the EPL,falling from around 400 in 1992 to around half of those numbers in recent years.

Some interesting trends tied to the expansion of the nationalities of the EPL managers can be noted in the figures with both French,Spanish and Portuguese players becoming more prominent in the noughties.Also the recent surge in the purchase of outstanding African qualified talent and and increase in players from traditional powerhouse countries such as Argentina and Brazil can be spotted in the various graph.

(The scales used on some graphs aren't always consistent,but most countries would barely register if this wasn't the case.So just check the vertical axis before comparing graphs.Drag the slider at the bottom left of each graph to see all the countries featured).

How Many Players from Great Britain and Ireland have Started at least One EPL game over the Last 20 EPL seasons.




How Many Players from the Rest of the World have Started at least One EPL game over the Last 20 EPL seasons.





How the Proportion of European and Home Countries in the EPL has Changed over the Last 20 seasons.




How the Proportion of Non European Countries in the EPL has Changed over the Last 20 seasons.




How the Proportion of Nationalities in the EPL have Declined or Risen over the Last Two Decades.




How Recruitment in the EPL has shifted away from Europe towards Africa and the Rest of the World over the Last Decade.



Friday, 1 June 2012

Strikers Shouldn't Be Afraid To Miss.An Appreciation of Robin van Persie.

As the seasons draw to a close across Europe the process begins of evaluating players for end of year awards or as potential transfer targets during the next transfer window.Inevitably the main spotlight falls on attacking players and goalscorers and the way in which these type of positions are judged is gradually changing as a result of the availability of more extensive data.Where there was once simply goals scored and games played anyone can now access more informative granular data such as shots,shots on target and shots to goals ratios.

Excellence in any form rarely requires numerical verification,so it seems sensible to start with the acknowledged best and review their statistics in an attempt to spot any indicators of potential greatness.Each of the top clubs possess fine strikers,but as this year has demonstrated,few are better than Arsenal's Robin van Persie and he was equally impressive last season when he scored 18 times at a rate of almost a goal per starting appearance.I'm going to use van Persie's scoring statistics from 2010/11 when he contributed 18 Premiership goals to Arsenal's seasonal total of 72 using data kindly provided by OptaPro.

Van Persie made 25 appearances in the Premiership for Arsenal in 2010/11,including six from the bench.His 18 goals came from 85 attempts on goal,neglecting 12 blocked efforts,so his strike rate was an impressive 21%.Of his 85 attempts,43 either ended up in the back of the net or required the keeper to make a save,so his accuracy of 50.5% was equally noteworthy.

If we compare van Persie's shooting a scoring prowess to his fellow Arsenal strikers and midfielders,including the likes of Fabregas,Arshavin,Nasri and Walcott we find that he leads his teammates in both categories.The rest of the team minus the defenders hit the target with just 49% of their combined attempts and scored only 13.3% of the time.

Van Persie's Shooting and Scoring Efficiency Compared to that of his Fellow Midfielders and Strikers.

2010/11
Season.
% of Shots
on Target.
% of Shots
that Resulted in Goals.
Robin van
Persie.
50.6 21.2
Arsenal's Other Midfielders & Strikers. 49.1 13.3

We shouldn't really be surprised at these figures,Robin van Persie is primarily a goalscorer and a big part of that talent is an ability to convert chances.Combined with his superior accuracy,he appears to possess the classic requirements to be a top striker,namely an ability to hit the target and lethal finishing.However,these raw numbers may be deceiving and with further investigation another less obvious and potentially important facet of van Persie's talent and personality may become apparent.

Nearly a quarter of van Persie's goal attempts were made from a distance of ten yards or less compared to just 16% of those attempted by the other Arsenal players and it seems reasonable to assume that hitting the target in a fluid sport such as football becomes more difficult the further away you are from goal.Using OptaPro's 2010/11 seasonal shooting data for van Persie and his colleagues I've used regression analysis to project how likely it is that each group firstly scores and secondly hits the target from varying distances.

How Likely Arsenal Were to Score from Varying Distances Based on 2010//11 OptaPro Data.


The data is quite naturally sparse as we move further from the goal and the line of best fit is only a approximation,but van Persie's preeminence amongst his team as a prolific converter of chances is confirmed.His projected conversion rate is superior for the entire range of distances from the penalty area and beyond.If goalscoring is a talent,this graphic demonstrates that van Persie certainly possess it and given the choice of a chance falling to either him or a another random Arsenal player,van Persie should be the choice.

Again this merely confirms RvP is an excellent striker and we already knew that,but the second graphic may go someway to shedding new light on how he is so successful.A large proportion of van Persie's goal attempts are made close to the goal,25% are within ten yards and the closer you are to a target the easier it is to hit it.If we run another regression on how likely it is a shot will hit the target with varying distance,we see that van Persie is actually less accurate than his teammates at most shot distances.His overall superior accuracy of 50.6% compared 49.1% that we saw in the first table results from his shots on average originating from closer to the goal than those attempts from other Arsenal players.

How Likely Arsenal Were to Hit the Target from Varying Distances Based on 2010//11 OptaPro Data.


So now as an Arsenal fan if you want to see the opposing keeper have to attempt a save you are slightly better off if the chance falls to a random Arsenal attacker or midfielder rather than the team's consistent leading scorer.

These results are from one season and just one team,so they may not be repeated over other seasons or in larger sample sizes,but potentially we have a tremendously talented striker who is better than his teammates at converting chances regardless of shot distance.However,he is also more likely to miss the target completely than are a group of comparable colleagues at all distances until the rates converge around 30 yards from goal.

One of the qualities that former England coach Sven Goran Eriksson looked for in his players was an absence of fear of failure and perhaps the numbers we are seeing here shows that van Persie has this trait.His "poorer" accuracy at all distances compared to his colleagues may be because he is prepared to shoot early or aim for the areas of the goal where the margins for error are small.His more conservative teammates may be inclined to play safer and be content to initially force the goalie to make a save.Van Persie's longterm payoff from being free of any anxiety caused by an increased "failure" rate for accuracy may be an increased successful goal conversion rate because his on target shots are more difficult to anticipate or save.

We are conditioned to look at performance indicators and assume that increases in efficiency is always the way to go,but perhaps in the case of goalscoring an inferior rate of shooting accuracy is actually the driving force behind an increase in the ultimate aim of increased goal conversion rate.Is the coach's maxim of "Don't be afraid to miss" being embraced by the very best?