Keeping Your Defence Healthy.

Recently I wrote up a method to quantify the effect of injuries on a side at Pinnacle. The number of matches a player was unavailable for was weighted to account his value to the team to obtain an alternative squad value for each Premier League in 2014/15.

Therefore, a £20 million player who was absent for 10 matches would in theory be more keenly missed than a £5 million player who was absent for the same span of games.

Under this method Everton were the team who appeared to be most inconvenienced through losing valued players for long periods of the season, while Leicester lost the smallest weighted proportion of their squad value.

On average, a side lost 17% of the value of their squad over a season to injury, although other causes, such as international tournament all ups and suspension also impacted on the availability of players.

So even though injuries are the staple of much Premier League coverage, they are only one part of the reason why a side may be considered to be under strength and even the most accident prone team doesn't stray too far from the baseline injury rate for the league as a whole.

Injuries are a shared experience for all teams and had Everton been more commonly lucky in the treatment room, they might have expected to gain an average of a couple of extra points per healthier season.

The media coverage reaches its most strident when the absentee is a forward. Understandable if the missing star is worth say £49 million, but the majority of teams either don't have the luxury of such players or if they do, squad depth often allows a similar quality of replacement. But less importance is placed on absentees from either midfield or defence.

Where the Injuries Occurred During the 2014/15 Season.

Team	% Forward Value Lost to Injury.	% Midfield Value Lost to Injury	% Defensive Value Lost to Injury
Arsenal	13.8	32.3	15.3
Aston Villa	18.6	12.2	23.5
Chelsea	19.3	11.5	4.9
Everton	17.9	30.7	21.2
Liverpool	30.0	12.2	21.9
Manchester City	15.7	14.6	12.4
Manchester United	17.3	17.5	30.6
Newcastle	9.3	33.0	23.2
Stoke	28.8	8.8	13.8
Sunderland	6.9	28.1	11.3
Tottenham	9.2	4.7	19.2
WBA	14.3	8.9	19.4
WHU	36.3	11.2	21.0

The table above highlights where the largest injury burden fell during the 2014/15 season on teams who have been Premier League regulars over the recent past.

West Ham, Liverpool and Stoke were the sides who saw their offensive value degraded proportionally the greatest by longterm injuries, losing respectively Carroll and Sakho, Balotelli and Sturridge, and Bojan and Odemwingie for in excess of a season's worth of matches.

And Manchester United, Villa and Newcastle suffered greatest on the defensive side of the ball. All bar one of Villa's defensive squad players were unavailable at some stage of the season and the other two sides suffered similar levels of disruption, meaning the teams not only lost squad value from their defence, they also had to continually shuffle their defensive pack.

In contrast, Chelsea had six defenders who were ever present for selection and the most number of Premier League matches one of their defenders was unavailable for during 2014/15 was four games. So the eventual champions had both defensive stability if they so wished, as well as ample choice.

Mame Biram Diouf inadvertently degrades Wrexham's defensive value.

It is tempting to try to see if defensive or offensive injuries have a greater impact in decreasing a side's subsequent performance. However, methodology is problematical. Using bookmaking odds may use estimations which have already been tweaked to account for injuries and creating a proprietary performance model is beyond the resources of most.

A simpler alternative may be to compare the seasonal performance of regular Premier League sides to their historical average and then see how this over or under-performance correlates to their defensive and offensive injury burden.

For example, Arsenal's 75 points in 2014/15 was in line with their average points per season for the previous 10 campaigns, while the two Merseyside teams under-performed their par from the last 10 years, as did Newcastle.

Loss of attacking value due to injury shows little correlation with a the graded performance of Premier League regulars during the last completed season. Liverpool under performed under the sternest of attacking injury loads, but Stoke prospered against their traditional points average despite similar offensive losses.

However, there does appear to be a relatively strong correlation between the amount of seasonal defensive disruption and a poorer than usual performance. 

The five Premier League regular members who lost the most defensive squad value due to injury in 2014/15 each under performed against their 10 season average points total, averaging an under performance of over 17%. While the five sides who largely escaped injuries to defenders all performed either to previous average expectation or exceeded it, on average by 12%.

 

A single season and a general trend linking better performance to a healthier defence is not definitive, but there are sound reasons to support the proposition. For example, organisational skills are often cited as a significant factor in defensive competence and familiarity bred from a settled and consistent defensive unit under a low injury load is likely to assist this.

Injury reports may be only slightly more newsworthy than transfer window speculation, but it may be worthwhile to take note when the list is peppered with defenders.