Tuesday, 9 October 2012

Worrying Times For Liverpool At Both Ends Of The Pitch.

The recent explosion of available English Premiership data has provided a route for the curious to begin to examine in much more detail the core actions that go towards deciding the outcome of a football match. The Laws of the game award the victory to the team scoring the most goals, so it's sensible to roll the goalscoring process back one stage to try to see which teams are making the most of their scoring opportunities and equally importantly which defences are making scoring difficult for opposing strikers.

How efficiently teams turn goal attempts into shots on target and ultimately into goals often defines where a team ultimately finishes in the table. With access to x,y data points for shooting attempts it is now possible to compare team performance in this area against an average basket of hopefully, representative teams from the EPL. At the very least we should be able to highlight a side's strengths and weaknesses compared to par when dealing with goal attempts or dishing out shots of their own. This is the so called descriptive use of data, projecting suitable regressed figures for use in predicting future performance may come later.

The rolling TV soap opera that is Liverpool's seemingly constant battle with insufficient reward from copious amounts of toil in front of goal again provides an idea test case for this type of analysis. The Reds currently languish on the fringes of the relegation battle, with a negative goal difference (even after a five goal rush at Norwich) and question marks regarding their inability to adapt to a new style of play and also over the form of Pepe Reina.

Shot analysis has made great strides in recent seasons. Analysis no longer has to rely on weight of numbers to even out the quality of the shooting opportunities under investigation, but such unknowns as the position of defenders and the pressure that is being applied to the shooter are still largely absent. So with these caveats, let's look at how Liverpool have fared so far in the EPL.

Using the Opta powered Fourfourtwo app I've recorded the co ordinates of all 123 goal attempts made by Liverpool so far this season and designated each attempt as either "on target", "off target", "blocked" or "a goal"  (a goal is also recorded as an on target effort). By comparing the expected outcome for Liverpool's 123 shots, had they been attempted by an "average" EPL team, with The Red's actual outcomes, we can try to gain a better understanding of their season to date.

Shot Expectancy And Actual Outcome For Liverpool's Attack and Defence. 2012/13 To Date.

Team Expected No. of Shots On Target. Expected No. of Shots Blocked. Expected No. of Goals.
"Average EPL Team" 39 31 10
Actual No. Made By
L'pool Attack.
29 33 9
"Average EPL Team" 24 21 6
Actual No. Allowed
By L'pool Defence.
24 21 12

Looked at over the season so far, there initially appears to be a clear pattern of average performance from the attack because their 123 shots have produced nine goals, just one less than our baseline model predicts for an average team playing similarly average opponents. However, there should be accuracy concerns because Liverpool's shooters have hit the target 29 times compared to an expected 39 and whereas it is possible that the score of 29 is the luck driven outlier, it may be that it will be the goals that begin to fall into line with the wayward shooting.

Based on goals scored Liverpool are about an average attacking side, but shots on target may suggest that currently they aren't quite that good.

If we now move onto the defensive qualities of the side. All conclusions should be tentative after even 100+ shots, so Liverpool's defensive record of dealing with opponent's shots, based as it is on 77 attempts should also be interpreted warily. But from a purely descriptive "this is how we got here" approach the expected goals column stands out.

How accurate a team can be and how quickly their attempts are closed down and blocked is down to a combination of their individual talent and the actions of the defenders. So if we accept that Liverpool have faced a fairly typical cast of opponents so far, defensively, as a unit they are around average at closing down shooters. However, they have conceded double the expected number of goals.

Video analysis would help to decide the cause of this shortfall in goal prevention. It's easy to solely implicate the keeper. But individual mistakes from players in front of him leaving opponents with clearer cut goal attempts or an unusual, but not prohibited run of (poor) outcomes occurring randomly with little actual change in Reina's ability should never be ruled out.

Liverpool's Attacking Record By Game Compared To An Average EPL Baseline.  

Team Expected No. of Shots On Target. Expected No. of Shots Blocked. Expected No. of Goals.
Average Team. 5.1 4.0 1.3
Actual No. v WBA. 2 7 0
Average Team. 5.0 4.8 1.2
Actual No.v Man City 3 5 2
Average Team. 6.0 4.8 1.5
Actual No. v Arsenal. 4 4 0
Average Team. 7.2 6.0 1.9
Actual No. v Sun'land 6 4 1
Average Team 4.8 3.3 1.3
Actual No. v Man U. 6 2 1
Average Team. 5.4 3.7 1.7
Actual No. v Norwich. 6 6 5
Average Team. 5.5 4.8 1.2
Actual No. v Stoke. 2 5 0

Once we start to break down seasons into game by game slices, the numbers begin to become as much a product of Liverpool's opponents as they are of Liverpool. Liverpool may have seen a lot of their shots blocked against WBA simply because The Baggies are extremely adept at blocking shots.

Few teams are currently well known for their ability to block shots, but we can make an more educated estimation around the goal based expectancy. It's likely that Liverpool under performed in the 90 minute stretches that made up the Stoke, Sunderland, Arsenal, WBA games and possibly during the ManU one, while they over performed in the Man City game and massively over performed during the Norwich match.

This illustrates the partly random nature of scoring. Teams can hope for an ideal distribution to provide a maximum points haul, but they have to deal with the distribution of talent based rewards that actually come their way, especially in a short sequence of games. Scoring five at Norwich when an "average on average" matchup would have produced just under two, but then under performing in the majority of other matches,  coupled with accuracy issues from the season long study, may suggest again that goal scoring will be the measurement that will fall more noticeably, rather than accuracy being the one to dramatically increase.

The reality is likely to be a combination of the two, with shots becoming more accurate, goals becoming slightly less efficient and the "new" Liverpool team gravitating to a lowly position within the top ten.

Liverpool's Defensive Record By Game Compared To An Average EPL Baseline. 

Team Expected No. of Shots On Target. Expected No. of Shots Blocked. Expected No. of Goals.
Average Team. 6.1 4.5 1.9
Actual No. v WBA. 6 6 3
Average Team. 3.4 3.0 0.8
Actual No.v Man City 3 3 2
Average Team. 3.5 2.8 0.8
Actual No. v Arsenal. 5 2 2
Average Team. 1.9 2.1 0.4
Actual No. v Sun'land 1 3 1
Average Team 3.0 2.0 1.2
Actual No. v Man U. 3 2 2
Average Team. 5.1 4.1 1.1
Actual No. v Norwich. 4 4 2
Average Team. 1.5 1.8 0.2
Actual No. v Stoke. 2 1 0

The same strength of schedule issues apply in a game by game look at the Red's defence, but the worrying fact is that six of their seven opponents have scored more actual goals than the expectation derived from a wider, hopefully average basket of matchps. The two Manchester clubs and Arsenal are clearly above average, but the balance is restored by the presence of Norwich, Sunderland Stoke and even the currently high flying Baggies. Once again on a game by game basis, collective or individual failings in defence appears to be a big factor in their current plight and may prove to be a vulnerability over the course of the year. Reina is certainly a keeper in the spotlight at present, along with a defence which appears uncomfortable playing the ball from the back.

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