Home Field in Divisional Games.

by Denis O'Regan.

Home field advantage exists in every professional sport.For example in association football in the UK teams acquire upwards of 60% of their league points at home and on average win just under half of their home games.Home field is worth around 0.4 of a goal.

However,if you restrict the soccer samples to local derbies then the figures look significantly different.Local derbies are contested between very close geographical rivals (usually,but not always from the same city).The games therefore are of great importance to the fans,the players are familiar with their opponents and their surroundings and travel fatigue is eliminated.

In such games goals overall are less plentiful and home field advantage appears to be greatly reduced.Home sides now only win around 40% of the games (there are more draws) and the average margin of victory for the home side is nearer to 3 tenths of a goal.

Divisional games in the NFL appear to share many characteristics with local soccer derbies.Travel times are shorter,the away team is familiar with their opponents stadium and with their opponents and the game has heightened importance both to the fans and to the team.To get to the post season you first must top your division.

I therefore compared the scoring in divisional and non divisional games since the league went to 8 divisions of four teams.

Scoring is depressed in divisional games compared to non div ones,but the difference is small.Non divisional games averaged 42.9 points per game compared to 42.2 ppg for divisional ones.

It's when you start looking at the margin of victory for the home sides in the two types of matchups that potentially significant differences become apparent.The average scoreline in divisional games is 22.0-20.2 in favour of the home team for an average home field advantage of only 1.8 points.That compares to around 2.7 points for the league as a whole over the same timescale and 3.1 points for all non divisional games,again since 2002.

Wins and losses also confirm the depressed HFA in divisional games.Home teams win just 54% of divisional games (which tallies well with the 1.8 point average margin of victory),compared to 58% for the league overall and 59.5% for non divisional games.

Divisional games appear to be just as atypical when you look at how the HFA is distributed over the 4 quarters of the game.It's long been established that HFA appears to be at it's strongest in the first quarter and consistently declines to be at it's lowest in the 4th.This is evident in non divisional games.

In these type of games 39% of the HFA is gained on average in the first quarter,35% in the second,19% in the third and 6% in the 4th.

However the divisional games don't follow this pattern.Comprising 680+ games,40% of the HFA is accrued in the 1st Q,31% in the 2nd,ONLY 5% in the 3rd and 25% in the 4th.

The average points scored are

1st Q,home side 4.6 pts,away side 3.9 pts.
2nd Q,home side 6.7 pts,away side 6.1 pts.
3rd Q,home side 4.4 pts,away side 4.3 pts.
4th Q,home side 6.2pts,away side 5.7 pts.

and these numbers are reflected in the win/tie/loss figures for each quarter.

1st Q,home side "wins" 42% of the time,away side "wins" 35% of the time and 24% of games are tied after one quarter.

Re setting the game to 0-0 at the start of the 2nd Q,home sides "win" 46%,away sides 40% and 14% are tied.(The lower rate of ties reflects the higher scoring in this quarter).

3rd Q,home side "wins" 39%,away sides 38% and 23% ties.

4th Q,home side "win" 43%,away sides 39% and 17% are tied.

It's easy and probably dangerous to attribute reasons for the closeness of the third quarter and the surge of home field advantage in the fourth compared to other non divisional games.(The team trailing at the half is more likely to be the visitor,realising the importance of the game,they make considerable adjustment at half time and "up" their game to get back into contention.However,the effort takes it's toll in the 4th and increased crowd involvement sees the home side well back on top).

Plausible,but probably not even half the story.The numbers may just be a fluke of nature and they certainly aren't mirrored equally across every division. (For example visitors dominate the 4th Q in the AFC North and away sides "win" that quarter over 50% of the time).

Further superficial investigation suggests that visiting teams in divisional matchups are more efficient at throwing the ball than you would expected compared to visitors in non divisional matchups and the home side commits more penalties than is usual.

Whether these game stats cause the wins or the wins cause the games stats is,as ever open to debate.