Wednesday, 24 April 2013

Leading When It Really Counts.

The fundamental building blocks of football analysis are fairly well established. Goals are the rare, but intrinsically valuable currency from which virtually every other match outcome can trace back their origins. Likelihood of winning, the outcome of most interest, is strongly correlated to the ability of each side involved in a game to score and prevent goals. The ability to explain the past and predict the future with reasonable accuracy, in larger enough game samples is well within reach.

Fortunately, shorter term variation from these expected norms are also common place and it is this random noise that prevents football from becoming a sterile exercise in number crunching. Consequently, a team which, for instance suddenly shows an elevated home field advantage may be recording these figures through random variation or through a fundamentally different approach at home compared to away. The temptation is to try to rationally explain the latter, when the cause is almost always predominately due to the former.

Time spent leading, drawing or losing hasn't really received the exposure of home field advantage or outright match results, but along with most data recorded in football, it can significantly alter the course of side's season by departing from the line of greatest expectation and help to deliver randomly driven season long highs or lows that are rarely repeated.

Teams cannot chose precisely how many goals they will score and concede over a set number of games, nor can they decide how those goals are distributed within games. But if they could the optimum return for a six to three goal count spread over three matches would be achieved by way of three 2-1 wins. A less favourable outcome would result if all six goals were confined to just one of the three matches. Similarly for lead time, three games where a first minute concession was only overcome by two injury time replies would result in greatly differing lead times compared to a scoring sequence where goals were scored early and conceded late.

So variation is to be expected, even in large numbers of matches and if this variation results in better than expected outcomes, we may overrate sides on the seemingly soundest of evidence, only to be disappointed when they revert to a level of results more in line with their actual skill levels.

Lead time, combined with goal distributions is a prime candidate for causing such miscalculations. As with goals, teams aren't entirely in control of when they lead during a match. Obviously and ideally a side would like to lead going into second half injury time and see the result through for three points. A team gets no added points for leading for a large portion of the match if they then succumb near to the final whistle. In short, is the ability to hold a lead for longer a better indicator of repeatable skill than the other extreme of gathering points with late winners ?

To try to answer this we first need to create a baseline which correlates time spent leading (and ideally drawing) to points accrued over a season. Modelling the data along the lines of this post from last year, appears to highlight a subtle difference in the importance of time spent leading for the poorer teams and the rest. A team with a winning chance of around 20% or less sees their chances of leading peak just after the halftime break, whereas those with winning chances of 20% or greater see their chances of leading constantly rising until the full time whistle.

For example, a side with a 10% chance of winning a game has a greater than 11% chance of leading that game after an hour.

By contrast strong favourites will see their chance of leading the game consistently rise until full time is reached.

The inability of poor sides to hold onto a lead when faced by much stronger opposition has implication for the use of time spent in the lead as an indicator of overall ability. The relationship between lead time and expected points is likely to be different for changing team quality, particularly for those poor sides which spend proportionally more of their lead time mid game (when no actual points are awarded) and less at the game's end (when they are).

We can produce average expected points for differing team quality derived from actual lead/draw time and actual points gained for whole seasons and equally for a single match. The most memorable game from last year's EPL was the last to finish, Manchester City 3 QPR 2. City spent little more than ten minutes leading this game and almost an hour all square. The majority of points scoring outcomes from games with these type of lead/ draw times are going to be draws, occasionally, as happened last season to City, a team will snatch an unlikely win.

Expected Points Based On Lead/Draw Time Comparable To Manchester City's Final Game With QPR.

Type of Team. Average Expected Points from Such A Game.
Big Four Side. 1.2
Other Top Ten Side. 0.9
Bottom Ten Side. 0.8

The ability of top four sides to lead when it matters is illustrated by the line of best fit for three types of team. A top side which had the lead/draw time in a single game identical to Manchester City in 2011/12's final game would expect to average 50% more points than a bottom 10 side under identical circumstances.

Lead/draw times are good indicators of expected points and possibly better future performance indicators than actual points totals, but they also depend on team ability.

On a game by game basis from last year, Manchester City's lead/draw time would have resulted in a typical big four team accruing 86 points, three short of City's actual total. So they gained three more points than expected. By contrast, United's lead/draw time resulted in 89 actual points compared to an expectation of 88. A case of City getting slightly luckier than United ?

The sight of poorer sides leading mid game, but losing when it really counts has been common theme of United's games this season. Newcastle, Villa and Southampton each led mid game, but United led at the final whistle. The champions trailed for over 100 minutes in those three games and led for less than 5 minutes, figures that would see even the best struggling to take much more than a single point on average, yet United ended up with all nine points.

Around par for the course last term, this time around United have stretched their points total way beyond repeatable levels with a glut of timely scores. By trailing to seven teams after an hour, but losing to just four by full time, they are respecting the spirit of what a team of their quality may expect to achieve, but hardly the letter of the law. A six and five split would be much nearer to a typical Big 4 expectation.

They deserve to be champions, but they have also been, at times extraordinarily lucky as well. Their current lead/draw time is characteristic of a side just approaching 80 points rather than one powering on towards 90.

It's most likely not a trick they will consistently be able to repeat.

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