May 19, 2019

Geek Speak: Why Every Yard Matters, The Relationship Between Yards & Points

One of the most important statistics in football is also one of the most basic – total yards. If you knew nothing else about two teams,  be it records, point spread, who was favored and who was the underdog or any other in game stat, but you knew who had the most total yards you would have a 75% chance of picking the winner.

Closer to home Clemson went 9-1 in games where they out gained opponents and 1-2 when being out gained.

It’s usually at this point that football savants remind me of the teams who gained more yards than their opponents and lost as proof that I’m “wrong”.  Maybe they feel like I’m taking the physicality and strategy out of football by assigning a value to each yard gained (more on this below), but really the point of this is to reinforce the importance of each and every yard gained or lost, emphasizing the importance of the physical nature and accompanying strategic moves that are part of the game.

Many prefer black and white, yes or no and disdain odds and/or probabilities.  The only metric they are interested in is points.  Getting more than the other team guarantees a win 100% of the time. Nothing else matters.

Yet if a team starts at its own 10, drives 40 yards, punts and their opponent is backed up inside the 10 the team gets 0 points for that drive – but those 40 yards have a value.  Field position has been changed, and so have the odds of winning because of those 40 yards that yielded 0 points.

Every yard is important, at least while the game is in doubt.

Clemson scored on offense, defense, and special teams in 2014.  However, the vast majority of touchdowns (and therefore points) came on offense (89.6% of Clemson touchdowns came on offense) and involved gaining some amount of yards.  Sometimes it takes a lot of yards, sometimes just a few, but by and large you score by gaining yards.

The graph below plots points and yards of every game over the last four years (between 2 FBS teams). The slope should tell you all you need to know.

Yards & PointsYes, there are outliers, but the picture tells a story in 3 words – yards equal points.

Better than that generic “yards equal points” phrase, we are able to determine exactly how many points a team can expect to score based on yards gained.  Even more intriguing than that is the close to perfect symmetry of the numbers below.  For almost every 11 yard increment one additional point can be expected.

Expected Points Per Total Offense

There are no exceptions, meaning there is no instance where gaining more yards means you should expect less points.  It sounds amazingly obvious, but you’d be surprised at how many football fans believe total yards is an irrelevant metric.

Of course, the yards you gain are only part of the game and are therefore relative.  You can expect to score 36 points if you gain 490 yards, but if your defense gives up 510 yards you will most likely lose.

That doesn’t mitigate the overall point, which remains valid – yards are important because the more yards you gain the more points you are likely score – without exception, statistically speaking – and that means the more likely you are to win.

Total yards is certainly not the only metric I use when determining win probabilities, but its an important one that I give significant weight in my calculation.


The Difference Between Winners and Losers

Below are the metrics across the 686 games between FBS teams for the 2014 season to this point. Bowl games will be added once complete.

First, here’s a look at the averages for each metric.  A couple of things stand out – the plays are almost equal, with winners running a paltry two more plays per game.  It’s what they do with those plays (Yards/Play) that matters.  Secondly, many people say total yards don’t matter. They do.  More on this in a minute.

By Category 2014

Here’s a look at home vs. away and favorites vs. underdogs.  56% seems a bit low given that most Power 5 teams have 1 or 2 “gimmee” games on their schedule.  When you look at conference games this number is traditionally much closer to 50%.  More important than playing at home  is being the favorite.  The old adage “the best team usually wins” is in large part true, assuming the best team is favored.

HomeAway 2014

These numbers show the % of teams that have the better number for each category.  For instance, the winning team has more plays in 54.8% of the games, more total yards in 77.7% of the games (told you yards were important) and higher yards per play in 79.6% of the games.  Yards per play and total yards are the two most important stats in my book.  Secondly, we often hear about “winning” the turnover battle.  Since 22.9% of the time the turnover battle is even it’s more important to not lose the turnover battle (win or be even) – 82.3% of winning teams are at least even on turnovers.PCT 2014

50,000 Foot View of College Football

The charts below tell the big picture story of college football from 2011-2013 and cover 2,116 games between two FBS teams.

Some things that I found within the data:

  1. Almost all categories for winners increased (far right column) over the 3 seasons.
  2. Losing teams had reduced numbers in most categories in 2013 compared to 2012.
  3. Turnovers have remained remarkably consistent for both winners – 1.3 per game across all 3 seasons – and losers (slight variation in 2013).
  4. Winning teams average more penalty yards than losers.
  5. While the losing teams yard per pass average has remained constant, the winning teams have increased their yard per pass metric 2.5% over the 3 seasons.
  6. Both have increased their yards per rush, but winners have increased at a higher rate.
  7. Average rush yards for winners has increased by 9.2% and yards per rush by 5.1% for winners from 2011 to 2013.
  8. Scoring is up for both winners (5.7%) and losers (2.9%).
  9. Both winners and losers have increased plays and total yards, but winners have increased at  a higher rate than losers.
  10. As a whole, these numbers tend to lead credence to the theory that offenses are moving faster and have the upper hand (known as the Saban/Bielema Complex)

These numbers lay the foundation for an upcoming analysis by Paul Chimenti who holds an MS in Mathematical Sciences with Statistics Concentration. Paul is using a statatistics package that will arrange offenses and defenses in “clusters” based on metrics from the 2011-2013 seasons.

Winning Teams

2011-2013 Winners

Losing Teams

Losers 2011-2013

Total Yards Matter: Clemson Version

On Tuesday I explained why total yards matter in the big picture of college football – total yards correlates to points at a much higher rate than other statistic in college football.

I realize however, that many of those that read this site don’t care about this stat for college football as whole, but rather what it means for Clemson in particular.  The answer: The same thing.

While the number of plays run for Clemson has a strong (but smaller) correlation to points, I’m struck by the other numbers below.  The passing stats have weak to almost non-exisitent correlation to points scored and the rushing stats all have negative correlations.

Clemson Correlations

If you think about it, the negative correlation to rushing numbers makes sense – for Clemson.  While the rushing game is important, the Tigers are much more efficient at passing and plays spent rushing decrease the overall efficiency of the offense (yards per play) even if the rushing plays are successful.

Running plays are obviously an important part of the offense and the analysis above made no distinction between a passing play when behind by 10 or a rushing play when ahead by 10.  Perhaps that is something I can develop at some point – analyzing these numbers by game situation.

The data also confirms what we learned in Tuesday’s post (total yards matter) and refines the findings for Clemson – Total yards (no matter how they are gained) and plays run are two key stats for the Tiger offense.

Geek Speak: Why Total Yards Matter

A few years ago I happened upon a now forgotten web site that attempted to prove that yards don’t matter in football. All that mattered was points. My first thought was, “Well, yards are how you get points most of the time”.

Turns out I was right (for once).

The site went on and on with examples of how and why yards don’t matter. As I recall it was the heyday of the Honey Badger and LSU seemingly won week after week by scoring on special teams and defense.

Great, that’s one team out of 120 (at the time). For the vast majority of the other 119 teams and in the vast majority of games yards do matter. As a matter of fact, they matter more than anything else.
For 2011 and 2012 in games between FBS teams (1,404 games in all), 76% of the time the winning team has gained more yards than the losing team.

It’s not rocket science.

What I didn’t analyze at that time was the correlation between yards and points scored.

Points seem kind of important, so I decided to find out which of the statistics I track most likely leads to points.

Out of the 12 (other than points scored) numerical categories I track, there is no greater correlation to points scored than total yards and, with the exception of yards per play, it’s not even close.

Total yards may not matter in a single game, season or perhaps (stretching a bit) for a particular team for some period of time, but in the big scheme of things if you want to know who is going to score more points figure out who is going to gain more yards.

Using the Pearson Coefficient I came up with a correlation of 0.766324 between total yards and points. You can read more about the Pearson Coefficient here, but the basic concept is a coefficient of 1 means there is a perfect positive correlation between the two variables and -1 means there is a perfect negative correlation between the two variables.

Yards and Points

What does this tell us? There’s not a better predictor of points scored than yards gained.

Anything above 0.5 can be considered a high correlation.

The interesting numbers to me are the ones that are typically associated by coaches, announcers and writers (and bloggers) as important to winning with low correlation to points scored like plays run (technically this falls in the medium correlation range), time of possession and penalty yards.

Remember that correlation should not be confused with causation. For example, the number of passes thrown has a low (and negative) correlation to scoring points, but the number of passes a team throws may not necessarily be the cause of the number of points scored.

Finally, when I do an analysis of this type invariably someone asks, “What about defensive statistics?” Defensive numbers are included in these statistics in this way: For every yard an offense gains a defense gave that yard up. For example, one would expect a given team to have less yards against Alabama and therefore less points. If an offense averages 500 yards a game and then plays Alabama, for example, they’re likely to gain less yards and score fewer points.

What we know from this analysis is that over the last two years a point is scored (or given up by a defense) for every 14.2 yards gained (or given up by a defense) on average.

This analysis included both the statistics of the winning and losing teams in 1,404 games, 2 teams in each game and 2 variables (points and total yards gained) for each team per game.