Sunday 9 June 2013

Is Shooting Easier On The Road?

There is a perception that a side adopts a more defensive outlook when playing away from home compared to games played at their home stadium. Certainly one slightly unfair barb aimed at Stoke's former boss, Tony Pulis was that he tended to setup with a packed defence, where the primary aim and duty of the majority of the team was not to concede a goal and very little team resources were committed to attack......and he was even more defensively minded on the road.

The general defensive outlook shown by visiting teams can be rationalized if we look at the average game state for home and away teams at the kick off. The average home side takes about 1.6 points from a match under three points for a win, compared to a shade over one point for the visitors. Therefore, on average at the start of the match, the one point currently owned by the visitors is relatively close to the longterm expectancy in terms of league points gained, but the hosts often start the match expecting more. In short, the visitors are happy with the current game state, the hosts, less so.

If away sides on the whole are more content to hold station for longer periods of a match, we should be able to see some of the effects of this more defensive approach in the more granular data, most notably shooting statistics.

X, y data that incorporates the field position from where the shot was taken, currently doesn't include any detail regarding the defensive pressure faced by the shooter. However, we should be able to spot the effects of this defensive pressure if we look at shots where this pressure is more likely to be present. If our assumption that visiting teams, at least initially set up in a defensive way and the average time for the first home goal to arrive is someway into the second half, we should expect visiting teams to be defensively orientation for longer than their hosts.

So I incorporated a variable for venue in my x,y coordinates, shooting model to see if the term was a significant factor in determining how likely a shot was to result in a shot on target, a block or a goal. Venue, it appears, does alter the likelihood of the outcome of a shot. Away from home compared to at home, shots from identical field positions are slightly more likely to result in goals, more likely to be on target and less likely to be blocked. Below I've listed the probabilities for each of the three outomes for a variety of shots from different positions on the pitch.

Venue Specific Shot Probabilities Based on Shot Location.

Venue. Vertical Distance from Goal. (yards) Horizontal Distance from Centre of Goal. Chance of a Goal.% Chance of a Block.% Chance of Shot on Target.%
Home. 28 10 1.5 40 19
Away 28 10 1.8 35.5 23
Home. 12 12 5.9 24 31.5
Away. 12 12 6.8 21 36.5
Home. 8 0 21.4 20.2 38.7
Away. 8 0 24.3 17.3 44.2

The model is constructed around thousands of actual shot outcomes using the x,y data of each shot position and adding a venue variable, at least in this dataset, is a statistically significant addition, implying that scoring is easier from identical pitch positions for the travelling side. It is not much of a leap to consider the amount of defensive pressure, both in the build up and the execution is less onerous away from home.

Of course, shooting efficiency is just one factor that contributes towards actual scoring records. Home sides score more goals on average than away sides because circumstances may make shooting away from home slightly easier, but the home sides have more attempts. 55% of shots are made by the hosts.

1 comment:

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