Wednesday, 24 October 2012

Is Shot Blocking A Talent ?

The gradual availability of data relating to events that occur during a match has allowed for a more detailed examination of the ways in which goals are both scored and prevented. Save percentages for keepers are now commonplace and increasingly shots, the precursors to goals can be broken down into sub categories such as on target and off target efforts and also blocked shots. Distance from goal and pitch co ordinates are still  a relatively scarce resource, so at the moment the most productive approach relies on the use of accumulated shot data.

Blocked shots are probably the most neglected of the readily available data, but they account for the fate of almost a quarter of football's goal attempts and can shed light on the choices being made by strikers and the skill sets that may be possessed by defenders.

On average an EPL team will face or attempt over 500 goal attempts over the course of a Premiership season, but even these numbers are mere samples of each team's likely true ability. The actual percentage of shots that either a defence blocks or an attack has blocked over a season will be made up of a combination of randomly blocked efforts and possibly occasions where the skill of the shooter or the blocker has influenced the outcome.

So the first question we need to answer concerns whether blocking shots from a defensive perspective or avoiding blocks from an attacking one is likely to be a repeatable team talent. We can do this by assuming that the league average rate for blocks is shared by every team and then construct a typical spread of rates for blocked shots under these conditions of parity of "talent". If the spread we actually see deviates from that expected by pure chance we can deduce that other factors are present, either individual player talent within teams or a tactical approach that encourages blocks.

Based on the team records for blocked shots from the MCFC lite dataset, the raw attacking and defensive rates appear to indicate the spread isn't consistent with blocking of shots being a purely random process. Some teams possess qualities or setups that see them block or avoid blocks at rates that suggest a skill is involved, especially on the defensive side of the ball.

The Percentage Of Blocked Shots For Attacking Sides In The EPL 2011/12.

Team. Raw Blocking %. Regressed %.
Liverpool. 22.8 24.6
Chelsea. 23.6 25.0
Stoke. 22.9 25.1
Norwich. 23.5 25.2
Aston Villa. 24.2 25.6
Arsenal. 25.9 26.3
Everton. 26.7 26.7
Wigan. 26.6 26.6
Wolves. 27.1 26.7
Snderland. 27.3 26.9
Man Utd. 27.2 27.0
Newcastle. 27.4 27.0
WBA. 27.6 27.1
Spurs. 27.5 27.1
Blackburn. 27.8 27.2
Fulham. 27.7 27.2
QPR. 28.6 27.6
Swansea. 29.0 27.7
Man City. 28.7 27.8
Bolton. 30.7 28.5

We can also use these results to regress the extreme performers, both good and bad towards the league average based on the number of shots they faced or attempted. If the skill is repeatable the season on season correlation is much more likely to be seen in these regressed figures. The first table shows how good teams were at avoiding seeing their shots blocked and there appears to be little correlation between this talent an final league position.

Liverpool top the chart although their striking woes were well documented and successful sides such as Chelsea and Arsenal follow them home along with lesser lights such as Norwich and Villa. That's not of course to imply that a marginally improved ability to avoid seeing you shoot blocked isn't unimportant. Villa for example may owe their Premiership survival to the couple of extra shots that made their way through a forest of legs to possibly find the target. A team's overall record, good or bad is a product of a wide range of footballing talents of which shot blocking is just one.

The Percentage Of Shots Blocked By The Defence In The EPL 2011/12.

Team. Raw Blocking %. Regressed %.
Sunderland. 31.3 30.0
Everton. 31.5 29.9
Stoke. 30.1 29.0
Aston Villa. 29.9 29.0
QPR. 29.5 28.7
WBA. 27.7 27.4
Man Utd. 27.5 27.2
Man City. 27.5 27.1
Spurs. 26.7 26.7
Liverpool. 25.9 26.2
Newcastle. 25.4 25.8
Bolton. 25.5 25.8
Norwich. 25.4 25.8
Swansea. 25.0 25.5
Fulham. 24.9 25.4
Arsenal. 24.2 25.1
Blackburn. 24.1 24.8
Wolves. 24.1 24.8
Wigan. 23.5 24.5
Chelsea. 23.2 24.4

Defensive blocking ability appears to be more unevenly spread between teams. This may be because so teams have exceptional blockers or they adopt a packed defensive style or frustrate opponents into attempting more long range efforts that are more likely to be blocked. Blocking rates for individual players are currently impossible to calculate because although numbers of blocks made by players are available we can only guess at how many attempted blocks they were involved in. So rating individuals at the moment will have to rely on raw counting stats.

Stoke's three best blockers of a shot line up for duty in a defensive wall, while Ric & Crouchie seem less keen.

Stoke are once again towards the top of the table in terms of effectively blocking an opponents efforts and their style of play in 2011/12 certainly involved getting bodies behind the ball. Their three most prolific shot blockers, based on raw numbers, Whelan, Shawcross and Huth invariably made up part of a defensive wall. Of course they may have combined to blocked many efforts precisely because they were often used in the wall or they may have been used in the wall because they had shown great aptitude at anticipating and blocking shots...........

1 comment:

  1. Many years ago there was a defender in my local team who blocked an unusually high number of shots. I put it down to the fact that he didn't mark as well as he should, meaning his opponents got the chance to shoot more than they should. Plus, he was clearly a liitle overweight.