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Thursday, April 26, 2007

Charting Our Progress - Time of Possession

Today we look at another of college football’s great axioms – time of possession, in our charting the progress series. I’d harbor a guess that this was one of the most discussed (or at least mentioned) variables during the Osborne era. Win the time of possession, win the game. Right? Maybe not.

According the work of SMQ, this statistic means very little, only slightly more than yards penalized in college football.

Here is what SMQ’s tables tell us about time of possession:

Really not much to look at there. Time of possession, just doesn't seem to be all that important in college football. Or at least it wasn't in 2006.

So it appears we have another reason to turn the volume to mute during televised college games – too much discussion about a variable that just doesn’t seem to matter. But why doesn’t time of possession matter like we think it should? Well there are actually already some pretty good explanations already out there, so let’s start with those.

First we have a fantastic rant from Brian at MGoBlog from a point last season in which Michigan was leading the nation in TOP (they ultimately finished 2nd behind Texas A&M).

Time of possession is a fraud. It is a fraud for these reasons:

You cannot "keep the ball away from your opponent" any more than a basketball team can keep the ball away from their opponent. When you score or turn the ball over, they get the ball back, no exceptions. Unless you attempt an onside kick, your opponent is getting the ball back after you're done with it. They will have the exact same number of possessions you do, plus or minus one depending on end-of-half and end-of-game hijinks.

It describes the actions of teams after they acquire a big lead and not what they do to get said lead. One of the primary reasons Michigan is #1 in time of possession: they've jumped out to massive leads in many games and cruised home. Opponents like Michigan State and Notre Dame have spent entire halves in a spread hurry-up emphasizing quick movement of the ball. Meanwhile, Michigan leisurely pounds the ball into the line until the game is over. Result: in the second half Michigan three-and-outs can take more time than 80-yard touchdown drives by the opponent. This is hugely distorting and tells us nothing more than "Michigan has a big lead."

It places undue emphasis on the run game. Michigan features a crushing ground game and a crushing run defense. Result: lots of Michigan runs and very few opponent runs. This naturally helps TOP, but the reason Michigan is good isn't because they possess the ball for relatively large amounts of time but rather those crushing units. Time of possession obscures the real reasons for Michigan's success.
Well played. I suspect TOP obscuring the real reasons for success can be said for a lot of folks. But we'll come back to that.

There is also real, academic research that also contradicts the implied importance of TOP. Harold and Daniel Sackrowitz in an issue of Chance, argued against the use of a ball-control, TOP-favoring offense. They claim:
that "a team using ball control may reduce the number of possessions and points scored by its opponent, but it will lose more often than if it did not use ball control."
In their study, the Sackrowitz team developed a mathematical model for evaluating the efficacy of three styles of play: unconstrained (a team's normal mix of offensive maneuvers and actions), time-consuming (using additional time), and hurry-up (using less time than normal).

Beware dorky math mumbo-jumbo ahead.
They modeled a typical time-limited game by a multidimensional Markov chain -- a sequence of random vectors, each of which can be written as a string of numbers. The first three numbers, or coordinates, may indicate which team has possession, the current point difference between the teams, and the amount of time remaining. The remaining numbers of a given vector could represent the values of other variables deemed important for the particular game being considered, such as the number of time-outs remaining. Such a vector describes the state of the game at the beginning of each possession.

Such a computational model allowed the researchers to check game outcomes over a broad range of possible situations involving weak and strong teams adopting different styles of play at different times. A consistent pattern emerged in all the cases studied: An unconstrained strategy is preferable to either the time-consuming or the hurry-up strategies for both teams, even when one team is demonstrably weaker than the other.
And what the hell does that mean?
"The results also force us to the realization that, despite what one feels emotionally, a proficient ball-control offense reduces the number of possessions for both teams," the authors note. "Thus, if anything, one might guess that the better team would decrease its probability of winning by using ball control, particularly if it had reduced its probability of scoring."
But what about seemingly irrelevant Super Bowls involving the Big Tuna?
In a 1993 New York Times article about football coach Bill Parcells, the reporter stated, "His masterpiece was the 1991 Super Bowl, in which his Giants defused the powerful and innovative offense of the Buffalo Bills through the simple expedient of denying Buffalo the use of the football."

The Sackrowitzes have a different view. "Even in the supposed ultimate endorsement of ball control, the 1991 Super Bowl, the Bills had ten possessions (but punted six times)," they remark. "In that game, a great defense helped to create the illusion that ball control is effective."
Hopefully you are at least starting to understand that time of possession is not a key to college football success.

Now let's look at Nebraska's time of possession under Bill Callahan.

Here we see some pretty amazing progress during Callahan's tenure. Unfortunately it is in a statistic that we have highlighted to be irrelevant to success. But wait, here is where it gets a bit tricky.

If we look at Nebraska in 2006 we will notice that the Huskers actually went 8-2 in games in which they won the time of possession battle. They were just 1-3 in games their opponents had the ball longer. So TOP does matter then in Nebraska, right? Wrong.

Time of possession is still a shaky predictor of success. It looks like the football equivalant of a "red herring". We think it matters, but research and a little better understanding of its ability to mask other, more important variables (that I will be focusing on later), allows us to see it a more appropriate fashion.

But for those that are still a bit confused, or who insist on hanging on to the importance of TOP, here is a bit more.
In 2006, Nebraska finished fifth in the country in TOP, but our record was just 9-5. Arkansas State finished one slot ahead of us at fourth in the nation. They finished the season with a 6-6 record.
In 2005 Nebraska won four games when they possessed the ball more than their opponent. The Huskers also won four games when their opponent won the time of possession battle.
It just doesn't matter. Or at least not to the degree we might think it does.