Under the Hood - NFL Penalties and Scores Posted on 08/25/17 : 0 comments
THE CALL ON THE FIELD
In NFL games, penalties can change the course of a drive and ultimately the outcome of a game. We typically hear that the more disciplined teams are better bets because they have less penalties during the game. In this week’s Under the Hood analysis, we will use historical NFL data to determine if statistics can back the claim.
APPROACH & DATA
We are interested to find out if there is a correlation between a team’s performance and the number of penalties or penalty yards the team has. We have two datasets for this analysis. The first dataset is the penalties. The penalties dataset contains the type, yardage, and offending of every penalty since the 2000 season. The second dataset is our game dataset. The games dataset contains teams points-for and points-against along with the total penalty yards that the team committed.
PENALTIES PER GAME
Before we jump into statistical calculations, let look at the distribution of a NFL team’s penalties per game.
First let’s look at histogram of penalty yardage. We can see that there is a bell-shaped curve for penalty yardage for a team. It is important to note that the distribution is slightly skewed with a mean of 52.114. The skewness coefficient is 0.719 and tells us that right tail of this distribution is longer than the left tail. This makes sense because it’s impossible to commit negative penalties.
If we look at just the number of penalties committed by a team in a game, we see a very similar distribution. The skewness coefficient for this distribution is 0.577, and like the yardage distribution, the distribution is skewed to the right.
Let’s check the correlation between penalties and penalty yards in a game. In the plot below, we can see that penalties and penalty yards are highly correlated. This makes sense, because the more penalties that a team commits, we expect a higher penalty yard total to be.
Let’s go one step further and see if there is a similar correlation between penalty yardage and a team’s performance. The plot below shows the correlations between a team’s score and the penalty yardage. Notice the contrast between the prior chart that shows a high correlation and this chart. In this chart, there isn’t any correlation between penalty yards and a team’s score. There is a very slight downward trend, however, this may be explained by the skewness of the distribution in the diagram.
Let’s look at all the variables in one chart to see if there are any correlations between penalties and scores. In the plot below, there isn’t a correlation between penalties and scores.
OFFENSIVE VS DEFENSIVE PENALTIES
Before we make a call on this, let’s compare the correlation between scores and the type of penalty (false starts, holding, etc). Maybe the big penalties have an impact on scores. First, we will look at common defensive penalties as they relate to Points Against for a team. The plot below shows that there isn’t any correlation between points scored and penalty yards.
It doesn’t look good for penalties as a predictor of scores. Before we make the call, let’s check the offensive penalties as they relate to points scores. Again, we see that there isn’t any significant correlation.
After further review, the call on the field is OVERTURNED. Penalties are not a statistical predictor of a team’s score. Simply using penalties to make your NFL bets would be a mistake. In future articles, we will dive deeper into penalties to find out if there other predictions that can be made with this statistic.