April 16, 2014

Geek Speak: The Importance of Pass Defense

Pearson 3

By now you’ve heard me say (or write) over and over about the importance of the yard per pass statistic on offense.  For those that haven’t, teams with a higer yard per pass number than their opponent win  81.1% of the time so far in 2013.

This can be thought of as an offensive statistic or a defensive statsitic: The better your team is at defending the pass (holding the opponent to a lower yard per pass number) the better chance you have at winning.

But of course, thats the old chicken or the egg argument: Is the losers yard per pass stat bad because they lost (i.e. throwing desperation passes in obvious pass situations) or did they lose because they couldn’t pass efficiently (just not very good at throwing and catching)?

My guess is a little of both, though I can’t prove it mathmatically and I’m not claiming causation.

What I can prove using the Pearson Correlation Coefficient is that yards per pass given up correlates highly to points given up on defense.  Higher than rushing yards, yards per rush or passing yards.

The stats below are for weeks 1-4 for 2013 for games between FBS teams only and shows the correlation between points given up to the various categories listed.  The closer the number to 1 the higher the correlation.

Defensive Point Correlations

Yards per rush and rush yards correlate highly to points given up, but yards per pass is the most important of the 5 statistics analyzed.

One would expect the negative correlation on turnovers – generally the more turnovers a defense gains the less points they give up, but I’m surprised at how low it is.  This analysis indicates that for the measures analyzed turnovers is the least important factor in points given up.

2012 College Football Statistical Summary

2012 Final

The 2012 season closely mirrored 2011 in terms of winning percentages of the categories we track. As you can see in the graph below many of the categories are very similar and some even overlap the other to the extent that it’s impossible to distinguish the two.

- 2012 Final

There are, however, a couple of categories where 2012 was vastly different than 2011: Turnovers and Penalty Yards.

In 2011 teams with fewer turnovers won 56.80% of their games. By definition this does not include games where the turnover battle was even, these games were not included on either side of the equation. In 2012 the team with fewer turnovers won 75.40% of their games – a whopping increase of 18.60% – a remarkable change in one year. The question moving forward is which year was an aberration, 2011 or 2012? On the flip side of that are penalty yards.

In 2011 winning teams had less penalty yards 52.16% of the time. Amazingly, in 2012 winning teams had less penalty yards only 43.37% of the time and winning teams actually averaged more penalty yards per game than losing teams. Not only that, but in perhaps my all-time favorite stat teams with 100+ yards in penalties were 55-33 in 2012 a winning % of 62.5% – higher than several of the categories we track.

In the big scheme of things two years is not a lot of history on which to base conclusions or identify trends. Still, we have 1,404 games currently in our database, which is not an insignificant number. The ultimate goal is to identify which stats are a signal and which are noise.


2012 Summary Final

College Football By The Numbers

20121211200620

As much of college football fandom has noticed scoring is up in 2012, but not as much as you’d think and most likely not where you’d think.

Winning teams are averaging 2.7% more points per game over 2011, while losing teams have upped their total by an average of 7.2%. Combined, that’s an increase of about 4.3% per game.

Incredibly, the average losing team is averaging just over 20 points per game. It seems like not to long ago that 24 or so points seemed to be the point where you had a very good chance of winning. Score 20 now and you are typically just an “average” loser.

Yards per pass is the best indicator of success in 2012 and there is a huge difference between what winners average and what losers average – 8.18 to 6.40. Winning teams average 28% more yards per pass than losers.

The key to offense is efficiency, not the number of plays run. The difference between winners and losers is only 1.59 plays per team, but winners average 94.50 more yards per game and 6.24 yards per play compared to 5.04 for losers. Think about that for a minute. Winners average 1.59 more plays per game, but 94.50 yards more. Efficiency.


2012 Summary15

The winning percentage for home teams dipped to 57.03% in 2012 and my gut tells me it’s around 50% or less in conference games. Early in the season home teams win at a higher rate, not because of a home field advantage, but because in large part the matchups are mismatches. For every Alabama – Michigan matchup there are 10 Clemson/Ball State type clashes. In the coming weeks I’ll be doing more research on this topic.

If there was any doubt, one look at these numbers tells you Vegas knows what they are doing. The favored team wins outright almost 76% of the time and the winning team covered over 74% of the time.

Penalty yardage is one area where coaches and fans are simply wrong, at least in 2012. Almost 57% of the time the winning team is penalized more (in yardage) than losers (54.16 to 48.89 on average).

One other note on penalties, almost inexplicably teams with 100 or more yards of penalties are 54-32 in 2012, a winning percentage of 62.8%.

Finally, the biggest change this year was turnovers. After years of coach speak about the importance of turnovers in winning and losing with dubious data to back that up, this year over 75% of the time winners had less turnovers than the losers and the winning team averaged almost a full turnover less than losers.

The graph below compares these figures for 2011 and 2012 and for the most part the numbers are fairly close and sometimes almost identical. However, there are two close to the right edge – penalty yards and turnovers – that changed dramatically this season as noted above.


We still have 35 bowl games to go before we can wrap up the 2012 season. At that point we’ll have a little over 1,400 games in our database.

Macro-Level View of CFB + Turnover Report

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As you may have guessed, there’s not much change from last week in the big picture, but turnovers continue to be the big story of 2012. This is an instance of coach speak coming true – winning the turnover battle really is having an effect on the outcome of games – and at a much higher rate than 2011.

Penalty yards is another interesting one to me – but this one is counterintuitive – not only have winning teams had more penalty yards in 2012, but teams with 100 or more yards in penalties are 28-16 this season.


2012 Summary6.1 The turnover report is another interesting one to me. Somehow, Texas A&M won a game in which they had 6 turnovers last week. Talk about your outliers. But overall this report shows exactly what you would expect – the more turnovers the less chance you have of winning. It also continues to show that while 0 turnovers are optimal, of course, 1 is not typically the tipping point. That designation belongs to turnover number 2, because when you have multiple turnovers your odds of winning are less than 50%.
Turnover Report12

Numerical View of CFB + Turnover Report

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We are now about 30% (based on the number of games) into the college football season and have a fairly representative sample size for the statistics and charts below.

An interesting move this week as the “Winning Team Covers” stat took a nose dive. In 2011 over 75% of the times a team won it covered the spread and that trend continued within a point or two into the first several weeks of 2012. This week it took a nose dive to just under 70%.


2012 Summary5
The other drop we often see as conference play begins is a drop in the “Home Team Wins” category. For the most part the cupcakes have been feasted upon and the home vs. away stat winning stat becomes much closer for the rest of the season.

The two stats that continue to amaze me (in relation to 2011) are penalties and turnovers. There was a slight uptick in teams with less penalty yards winning in week 5, but the number is still well below 50% and almost 9 percentage points behind 2011s number. Turnovers are by far the most changed category from last year.

Turnovers have been much more important in 2012 than in 2011 in terms of winning and losing. I have no idea why that is, but at this point it’s hard to imagine this stat reverting back to the 2011 number over the course of the season. With that in mind, I thought it would be a great time to do our “Turnover Report”, which shows the winning percentage for the number of turnovers a team has (independent of any other stats). Notice the precipitous drop when a team goes from 1 turnover to 2. That’s the point your odds of winning drop below 50%.

Turnover Report12

So when your team takes the field today, don’t be disturbed by the early turnover – be disturbed by the second turnover that happens later in the game – your odds of winning just plummeted.

Stats That Are Important

Besides the obvious – points scored – there are 6 stats that correlate to a 70% or better chance at winning. Some you would expect, some you wouldn’t, but the big one that is NOT on the list below is turnovers.

I explained a while back that while turnovers are important, they are far down the list of stats you need to be better at than your opponent to win the game. For example, have a lower yard per pass attempt average than your opponent and you have only a 21.18% chance of winning the game. Approximately 2 in 10. Lose the turnover battle and you still have a 43.20% chance of winning – more than double the odds of winning when you have a lower yard per pass attempt average.


Important Stats

The other note I want to make is that these are not solely focused on offense. Obviously, the better your defense the less likely the chance an opponent is going to average more yards rushing  or more yards per pass attempt.

Finally, headed into the 2012 season this appears to be a mixed bag for Clemson. We all know what the Clemson offense can do, averging 7.53 yards per pass in 2011. On the flip side, the Clemson defense gave up 7.30 yards per pass in 2011 and the Clemson Tigers aren’t very deep in the secondary, so that’s definitely something to keep an eye on.

Yards Per Completion and Yards Per Pass Attempt Trends

Tajh Boyd - Yards Per Completion and Yards Per Attempt

Conventional wisdom says Tajh Boyd’s problems started in the Georgia Tech game and have continued ever since and is now at four games.  The chart below shows a longer trend than most of us realized.  It appears Tajh Boyd peaked (at least in these categories) in the Boston College game and hit a season low and bottomed out last week against South Carolina.

Also, while the yard per completion numbers for UNC, Georgia Tech and Wake Forest were similar, they lag far behind the yards per completion numbers for the first six games of the season on average.

Boyd’s second worst yards per attempt average on the season?  Virginia Tech on October 1.

Tajh Boyd - Yards Per Completion and Yards Per Attempt