Sunday, December 24, 2006

Referees Influence Total Points Scored?

There is anecdotal evidence that referees do influence the total number of points scored in a game. Some crews are consistently more lenient on defenses than others (for example, if they call defensive pass interference or holding differently). The theory is that the referees are not biased against either team, but just have different interpretations of the NFL rules. And that players are aware of each referee's tendencies so they can score more points if the crew is offense-friendly.

Let's periodically look at this theory. One way to test it is to check the average points scored in a referee's games and check it against what we'd expect based on the teams involved, using the average total points in the team's games over the season.

Week 15:
Ron Winter (covering SD-Seattle): NFL average (41.1 total points), Expected from Ron's teams (40.3 total points), Ron's games (38.0 total points).

So Ron's actual total points is 3.1 less than the NFL average and 2.3 less than what you'd expect considering which teams were in his games.

Take this with a grain of salt, though, because both SD and Seattle have higher than average points per game (especially because the SD offense has the highest average points scored per game at 31.8 per game).

Ed Houcholi: his games have slightly less total points scored than usual: 2.6 points below the NFL average and 2.8 points below what you'd expect for the teams in his games. His total points average so far is 38.5 points per game.

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Saturday, December 23, 2006

Ongoing 2006 NFL referee statistics (Through 12/11)

This post covers our ongoing analysis of the 2006 season performance of NFL referees. Please post comments on the types of statistics you would like to see or any comments on the statistics we are already tracking.

Through week fifteen, December 18, 2006:
Ranking by penalties accepted, both teams:
Gene Steratore (14.8), Ron Winter (13.7), Tony Corrente
Peter Morelli (9.3), Walt Coleman (9.3), Bill Leavy
Wow, Peter Morelli's lead for lowest number of penalties accepted shrank dramatically in week 15. Now they are virtually tied.

Ranking by % penalty yardage accepted against visiting team
Gerry Austin (58%), Scott Green
Walt Coleman (43%),Gene Steratore
I am getting disenchanted with this statistic, because there is a negative correlation among the referees' % penalty yardage for visiting teams and the rate that the home team wins that referee's games. I would've hoped for a positive correlation, where a ref that helps the home team calls most of the penalty yards against the visitors. Oh well...

Ranking by home win-rate:
Bill Vinovich (73%), Mike Carey/Larry Nemmers (69%)
Walt Anderson (43%), Scott Green/Peter Morelli/Tony Corrente (46%)
I don't think anyone really believes that the referees are biased for or against home teams generally. But if you want to believe there is some unconscious bias, then watch Bill Vinovich's games and root for the home team.

After 4 weeks, the ranking (penalties accepted, both teams) was:
Mike Carey, Bill Vinovich, Tony Corrente, Larry Nemmers = top 4
Walt Anderson, Walt Coleman, Bill Leavy, Peter Morelli = bottom 4

In 2005: Bill Vinovich was #1 and Walt Anderson was last in total number of penalties accepted.

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Sunday, December 17, 2006

NFL Referee Statistical Tendencies (thru 12/11)

In this article, I examine which types of penalty statistics by referee seem to be based on the referee (and not just something random). The way I go about this is to see whether there is a correlation between the statistical breakdown by referee from weeks 1-7 and from weeks 8-14.

To put it another way, let's pretend that there are only three referees in the NFL and we compare the statistics for how often the home team wins. If we see a correlation of 1, then it seems like the statistic does relate to the referee. For example, if in quarter one 100% of ref A's games have home team wins, 50% of ref B, and 0% of ref C and we see the same statistics in the next time period, then it seems like it is related to the ref and not purely by chance.

Included are also the correlation values between the 1Q and 2Q of the NFL season (weeks 1-4 and weeks 5-8).

Let's see for a variety of statistics:
Largest correlations:
Penalties against visiting team (0.318) (1Q-2Q correlation was 0.237)
Total penalties (0.262) (1Q-2Q correlation was 0.376)
Penalty yards against visiting team (0.274) (1Q-2Q correlation was 0.188)
How often the visiting team has more penalties (0.242)
Total penalty yards (0.165) (1Q-2Q correlation was 0.363)

Very interesting -- there is a hugely negative correlation for the rate at which the home team wins. (-0.407) This suggests that the rate that a home team wins the game is not correlated to particular refs.

What does this suggest? Maybe the percent that a home team wins is not across-the-board affected by all referees. The variable that has a bigger correlation across-the-board to referees is the total number of penalties accepted in the game and the number of penalties accepted against the visiting team.

What does that mean? Some refs call more penalties than others and the discrepancies among referees' tendencies seems to exist throughout the season. So this suggests that some refs call the game differently than others in a consistent way through the season (or some believe in letting the players play while others tend toward enforcing the rules more).

On Replay Challenges: Using the statistics at Mike Sando's excellent blog at The News Tribune, I have run the statistics to see if there is a correlation between 1Q replay challenge reversal rate and 2Q replay challenge reversal rate. There is a correlation between 1Q and 2Q at 0.163 -- and see Mike Sando's blog for the full statistics (although he has not done correlation analysis).