The Usefulness Of Tackles.

Anyone who doubts the elevated regard in which attacking play is held in comparison to defensive talent need only watch an episode of Match of the Day. The day's worst defensive performance invariably appears first in the running order, while the best defensive show is aired, usually with poor grace in the show's final minutes.

Analysis of attacking play is also more heavily developed compared to the defensive side of the ball. Goals are the obvious end product of attacking intent, they alone decide the final match outcome and there is a well defined and easily quantifiable chain of evidence leading from goal creation to realisation.

Shots and shots on target are one step removed from an actual goal and correlate well with winning matches.  Assists come next in the chain, again providing a comfortingly strong correlation with success and it is only when we step even further back into the scoring process to look at mere, run of the mill passes that we begin to experience a more confused correlation between quantity and quality of execution and end product.

At the sharp end of goal scoring there is no compromise, a goal is scored (usually) when the ball crosses the line, but how we arrive at the successful conclusion can take on a multitude of different tactical approaches. Therefore, we eventually reach a point in the scoring process where there is no catch all statistic that can describe with equal clarity a possession based Barcelona approach or a direct, long ball plan.

Shots and assists can be used to illustrate a team's previous successes and partly predict their future expectations, but passes are more indicative of team tactics and such diversity often defies easy or relevant measurement.

Defensively the evidence chain is much shorter and potential for confused and weak  correlation is reached much quicker. Interceptions and tackles are widely regarded as the currency by which defenders are valued, but the reality is that these stats are much more the product of how a team is setup than how talented are a side's defenders. Tackles are the passes of the defensive world, they are not the equivalent of shots or assists. Tackles per minute were an irrelevance to the likes of Paolo Maldini because there are more ways to prevent a goal than there are to score one.

Bolton, A Successful Tackle or Just Buying Time?

A good starting point in trying to understand the part tackles play in the game is to see how often teams commit to a tackle. The risk involved in tackling is twofold. A mistimed effort can lead to cards and a failed attempt usually sees the tackler out of position, if not removed entirely from the rest of the attacking move. Sorting tackles by outfield playing position can give reasonable picture of where a team is making their challenges and in the table below I've corrected the figures to allow for playing time. Defenders or midfielders accrue over twice the playing time of strikers, partly through tactical substitutions and because they are more numerous in the lineup.

A straightforward totting up of tackles would therefore always see strikers trailing the other two positions, so I've corrected cumulative totals from the 2011/12 season to produce normalized per game figures for all three positions. The numbers should depend on the amount of tackling demanded of each position by each club and the requirement imposed on them by the opposition.

         Tackling Rates Per 90 minutes by Position, EPL Sides 2011/12.

Team.	Defenders.	Midfielders.	Strikers.
Aston Villa.	24	23	9
Manchester United.	23	25	10
Arsenal.	22	21	9
Norwich.	22	19	6
Manchester City.	22	18	10
Chelsea.	21	22	10
Stoke City.	21	18	9
QPR.	21	23	8
Wigan.	20	21	7
Sunderland.	20	25	10
Swansea.	20	22	9
Bolton.	19	21	16
Newcastle.	19	25	8
Liverpool.	19	22	13
Spurs.	19	23	10
Wolves.	18	17	10
Blackburn.	18	20	13
Everton.	17	19	8
WBA.	16	23	9
Fulham.	15	19	19

The baseline figure for team tackles is just under 19 per game. So Fulham's strikers were asked to tackle back at near league average team rates last term, almost twice the rate required of strikers as a group. A quality they may have sacrificed this term with the acquisition of Berbatov. They were followed in the tackling stakes by Bolton, anecdotally a side which defends from the front. In contrast, Stoke strikers are expected to contribute well below average tackling numbers, although regular Stoke watchers will know that Pulis demands pressure before contact as a tactic. Indeed Stoke's midfield also had the second lowest number of attempted tackles in 2011/12 and are only just in the top half of the rankings for defenders. Tackles are a component of defending, but not the only one and in the case of some teams such as Stoke, they are not the primary one.

Manchester United's commitment to tackles in 2011/12, both overall and particularly from defenders and midfielders is well illustrated. Last year's runners up required their midfield players to be able to tackle often, an attribute used by a variety of other teams ranging from Villa, Sunderland, QPR to Spurs, Chelsea and Newcastle. By normalizing tackling stats to the equivalent of a team consisting entirely of strikers, midfielders or defenders, season long playing styles by position become more transparent and may better highlight qualities required from various sides.

Overall there is virtually no correlation between tackle numbers as frequently exemplified by tackles per minute figures for individual teams and the ability to prevent goals, again indicating that raw tackle numbers are a product of tactics rather than proficiency. We need to look at tackling efficiency to see how effective these tactics are and how successful tackles may contribute towards goal prevention and ultimately help teams to win.

A successful tackle at worst slows down an opponents passing sequence and ideally teams would like to see a positive correlation between efficient tackling rates and goal prevention. Overall tackle rates usually lie between 70% and 80%.

          Percentage Tackling Success Rates by Position, EPL 2011/12.

Team.	Defenders.	Midfielders.	Strikers.
Arsenal.	75.1	72.9	80.8
Aston Villa.	73.9	76.9	79.5
Blackburn.	72.8	75.5	80.0
Bolton.	75.3	69.9	77.1
Chelsea.	77.1	76.5	82.8
Everton.	75.1	80.9	75.0
Fulham.	78.5	76.0	76.9
Liverpool.	74.0	73.2	75.3
Manchester City.	75.7	73.2	67.7
Manchester United.	77.1	71.3	87.3
Newcastle.	75.3	73.0	75.9
Norwich.	68.7	73.7	78.4
QPR.	73.1	72.0	69.2
Stoke.	72.1	68.0	72.0
Sunderland	78.1	75.7	69.6
Swansea.	73.8	71.2	71.0
Tottenham.	78.8	71.6	69.2
WBA.	73.4	77.6	78.8
Wigan.	72.3	73.4	85.3
Wolves.	71.9	76.8	80.6
Overall.	74.6	74.0	76.9

It's initially surprising to see strikers as the most efficient group of tacklers, with Manchester United's attackers particularly out stripping their defensive team mates. However, this highlights the danger of taking statistics at face value. Strikers are out numbered by other positions by around two to one in on field presence, so the smaller sample sizes are more likely to lead to extreme value either above or below the norm. Hence United's 87% success rate may not be repeated in larger samples, bringing rates closer to those enjoyed by the defence.

The higher overall figure for strikers as a group is likely to be because they can pick the tackles they attempt and sometimes opt for other defensive tactics, such as forcing a pass by closing down an opponent. Midfielders and particularly defenders are often required to attempt tackles that are the last ditch alternative to allowing a decisive pass or shot on goal. In short, tackle difficulty isn't well represented in these raw figures.

The correlation between team tackle efficiency sorted by position and goal prevention is non existent for strikers and possibly surprisingly, also for midfielders and it's only when we look at just defenders that a reasonable  correlation develops.

The efficiency of defensive tackles is the strongest tackling indicator of goal prevention beating out overall rates, rates for the other two nominal positions and raw tackle counts for defences. The relative weakness does indicate that other factors, most probably interceptions, applying pressure to induce errors and goalkeeping ability are also significant factors.

We can use a similar approach from an attacking perspective by recording the rates at which opponents complete tackles against individual teams to see if an ability to make defenders miss tackles leads to increased scoring rates.

The correlation in this instance is weaker, but the indication is that an ability of a team to make defenders proportionally miss more tackles tends to bring rewards with increased scoring. Low scoring sides from 2011/12 such as Stoke, Wolves, Villa, Swansea and Sunderland allowed opponents to successfully complete upwards of 75% of tackles attempted by defenders, while more free scoring sides such as Newcastle, Spurs and Arsenal made defenders miss more frequently. Both Manchester clubs were big outliers, accounting for the reduced r^2 values, with City particularly being capable of scoring extremely freely despite facing near average tackle rates from opposing defenders. Possibly an indication that City excel at overcoming other defensive tactics which are omitted from mere tackling data.

Both graphs can be combined to see how important tackles made and tackles received may be to the majority of EPL sides. Teams such as Chelsea, Arsenal, Manchester United, Spurs and Newcastle had defenders who tackled at above average rates and had attackers who induced opposing defenders to tackle at below average rates. This seemingly heady mix was translated into impressive finishing positions. However, Bolton and to a lesser degree QPR produce similar splits, but without the successful results. So once again we could conclude that tackle statistics are noteworthy, but incomplete predictors and possibly partly flawed.

To hint at why tackles aren't as indicative of success as say shots, we can look at Bolton's game against Manchester City from last term. Overall, Bolton made 19 tackles, 16 of which were deemed successful for a tackle rate of 84%. However, in just 11 of those 16 successful tackles were Bolton able to gain possession and try to develop a footballing move of their own. On five occasions Manchester City retained possession because the ball was put out of play for either a corner or a throw. It's churlish to deem an excellent touchline tackle as a failure, but tackles do come with varying degrees of success. Five times City were able to continue the move from very close to where a successful tackle was made, dropping Bolton's success rate from  84% to 58%. Similarly for City, they recorded nine success from ten tackles, but on three occasions Bolton retained possession from the resulting throw and a 90% strike rate fell to 60%.

Just as shot based models improve as we add details such as x, y co ordinates, tackling models may benefit from reference to the immediate aftermath of the challenge.

Defence is always more complex to describe numerically. Ways to defend your goal are more numerous, varied and sometimes in the case of pressing, difficult to record compared to scoring which ultimately boils down to a shot or header at goal. Tackling efficiency appears to be preferable marker compared to frequent but less successful tackle attempts and by grading different levels of success for individual tackles we may creep closer to identifying the great defenders from the merely good. While appreciating that some teams demand different approaches to defence where tackling may not be the primary priority.