Sunday, 27 September 2015

England 25 Wales 28

It seems churlish to distill down the most engrossing contest of the Rugby World Cup so far to a kicking contest, but so committed were the defence of both England and Wales that the try line was only breached once by each team and so kicking ultimately decided the fate of the first heavy weight encounter of rugby's initial experience of a "Group of Death".

Dan Biggar, a world class kicker with club and less often for country, save in the absence of Leigh Halfpenny was perfect from his seven penalty attempts and one conversion, while England's Owen Farrell was equally flawless from five penalties, a drop goal and a single conversion.

But the lingering controversy surrounds the penalty kick that never was from the right hand touch line, just outside the 22 which would have given Farrell the opportunity to kick the sides level with minutes remaining.

Instead England attempted to emulate, but failed to follow Japan's lead by kicking for the corner and the win, perhaps mindful of Wales' tendency to grasp defeat from glorious victory late in matches against the world's elite.

The generic chance of a kicker to succeed from where Farrell was required to kick the potential game tying penalty was around 60%, but Saracen's fly half raises the bar to just under 74% and until rugby stats become more widely available, we may only guess at how a points expectancy of 2.25 points from a touchline kick weighs up against a less likely haul of five or possibly seven points from a five metre lineout.

Ladies and gentlemen, your kicker for this evening.....Daniel Biggar.
Robshaw's decision to try to grasp the initiative in Group A partially eclipses the excellence of the kicks that were attempted and made on the night.

Both Biggar and Farrell were presented with a couple of difficult attempts mixed in with relatively straightforward tasks for kickers of their quality, but Biggar's extra opportunity, with the hindsight of knowing the failure of England's last driving maul makes Wales justifiable winners.

Simulating all kicks taken on Saturday, based around the position from where they were kicked on the pitch and the historical success rates of Farrell and Biggar, Wales win more points in 60% of simulations, with draws and wins for England roughly sharing the remaining 40% of outcomes.

However, if we throw into the mix Farrell's kick to the posts that wasn't called, England now win 41% of the simulations compared to Wales' 37% with 22% of the kicking simulations drawn.

And while context, such as the current score is inevitably missing from such an exercise, we can say that England did create the means to win Saturday's match slightly more often than they might have lost it, but they possibly chose not to use the fruits of their efforts to the best end......and Daniel Biggar's excellence did the rest.  

Additional research by @zanderk  :-)

Monday, 21 September 2015

The Third Law of Tottenham Hotspur.

A familiar sight for Spurs fans during the 2012/13 season was either Bale or Defoe peppering the goal with shots. The former hit the target on 70 occasions in the Premier League, scoring 20 goals and the latter was 40 for 11 goals.

For those who like their goals to come in a variety of guises, Bale was the one to watch, not only were his shots taken from a greater variety of distances than Defoe's, they also targeted a wider area of the goal.

A quarter of Bale's shots on target either entered the goal or required saving above the mid height of the net compared to Defoe, who virtually without exception aimed his shots low to the ground.

In terms of simply eye-balling the data, Bale had much more variety in his shot placement. If the goal were divided by high or low shots and then further by shots to the left, right or centre, giving six general shot placement areas in total, only one of Defoe's efforts in 2012/13 would have fallen into the "high" classification, compared to 19 for Bale.

Bale, ponders whether to go high or low.
Often it is useful to have a numerical value to express something that is self evident, in this case Bale's wider variety of shot placement in relation to his then teammate, Defoe.

Entropy, as any chemist will tell you is the measure of the disorder in a thermodynamic system and it is increasingly used to describe the amount of disorder in a sporting context.

For example, how competitive a league is may be expressed by calculating how similar are the league points currently won by all sides in the division. (Hat Tip to The Times' Fink Tank)

In all its gory, degree level, physical chemical context, entropy or S invokes eigenvalues, Boltzmann constants, usually close to absolute zero, but in a simplified context of Bale verses Defoe, the equation p*ln(p) is sufficient to extract a usable figure from the data, where p is a probability or perhaps a proportion and ln is the natural logarithm.

Shot Placement, Bale and Defoe, 2012/13 Premier League.

High Centre
High Left
High Right
Low Centre
Low Left
Low Right

It's a simple matter to convert the six possible shot placements for each player to proportions, for example Bale's 21 low centred shots comprised 0.3 of his total on target shots. applying this to p*ln(p) gives us -0.361, we may discount the negative sign.

In total all of the six possible placements for Bale add up to 1.62. Had Bale's placement been randomly shared between all six possible areas, the sum of each p*ln(p) would have been 1.79, so Bale's figure to describe how varied his attempts were is 91% of an entirely random placement selection.

In contrast, Defoe by virtually shunning any shots which required a keeper to raise his hands above his waist, scored only 58% in 2012/13.

Not only was Defoe fixated in hitting his shots low compared to the more diverse Bale, he recorded the lowest figure for any player to have hit the target 25 times or more during 2012/13.

The sample sizes are small, but Balesque players included Suarez, Aguero, Dzeko, van Persie and Cazorla, while Lambert, Nolan, Kone and Sturridge were players in the Defoe camp.

Penalty kick placement is an obvious use for a method that quantifies variety of choice. Gerrard had more variety than Lampard in where he aimed his career spot kicks, although my Gerrard data is incomplete, so that conclusion may change.

And scores related to pass direction for individual players or teams may be used to characterize team styles.

Thursday, 16 July 2015

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.

% Forward Value Lost to Injury.
% Midfield Value Lost to Injury
% Defensive Value Lost to Injury
Aston Villa
Manchester City
Manchester United

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.