Monday, February 11, 2013

Bad Defense or Bad Luck?

It took me about 24 hours to shake the bad feeling that comes with the realization that Allen Crabbe alone scored as many points in the game as the entire Arizona team in the second half.  The sad thing was that everyone knew what Crabbe was capable of, but  the Cats were powerless to stop it.  When you add in the 21 put in by Justin Cobbs, it was if we were beat by two guys.  It didn't matter who played defense. they just scored.

When a team does well or poorly, there are two sides to the coin, offense and defense.  Actually, this coin is four-sided because each team plays on both ends of the floor.  Let's just look at one simple aspect of this game- Cal's offense. The Bears shot an embarrassing 58.8%.  They also scored 1.15 points per possession, the most any team has managed against Arizona this year.   Is that because their offense was really good, because our defense was really bad, or was it some combination of the two?   This is not a simple question to answer.

If you think about it, when a team shoots well, it could be because they had many uncontested looks at the basket, i.e., bad defense.  It could also be that they made a lot of difficult shots under duress that they would normally miss.  In other words, the defense wasn't all that bad, but the Cats were just unlucky in that the Bears had a remarkably good (lucky) night of shooting.

To distinguish between the two, you need some independent measure of defensive effort.  I think time of possession can provide us some guidance here.  When the defense is playing really well, possessions tend to get dragged out.  Think of those classic defensive stands when the opponent has to chuck up a prayer at the buzzer.  Contrast that to a fast break uncontested dunk.  The first possession lasts 35 seconds.  The second lasts about three to five.  During good defensive efforts, the Cats spend a lot of time playing defense.

So, how do you measure time of possession?  Well, it's a little tricky, but it can be done using play by play stats like the one from last night.  I've been tracking these stats all season, but it wasn't until today that I decided that they might be of use.  By my estimation, the average Arizona possession lasts 16.3 seconds.  Our opponents' possessions have averaged 18.2 seconds.  To demonstrate that shorter possessions are generally a good thing on offense, the graph below shows the relationship between average possession length and points scored per possession for Arizona and our opponents this season.

This relationship is not strong, but I can assure you that it is real.  That point on the far right side is Utah.  They are outliers because they play a unique brand of slow ball.  The point on the top left?  That's the Cats against NAU when we held onto the ball for an average of less than 14 seconds per offensive bout, and we scored nearly 1.3 per possession.  I removed Utah from this plot, and added a trend line, which shows the expected offensive output for any team given the length of possession.

That yellow dot is the Cal Bears last night.  The average Bears possession lasted 18.42 seconds.  In a typical game, this would equate to an offensive output of 0.93 points per possession.  If the Bears had played to that level instead, they would have scored 72 points and lost the game.  If we measure the effectiveness of Arizona's defense in terms of the average length of Cal's possessions, it would rank 12th, or a middle of the road defensive game.  What this suggests to me is that California's offense was significantly better than what would be expected given Arizona's defense. 

This is kind of how the game felt to me.  Sure, Crabbe had some easy buckets, but many of them were contested.  Regardless, the shots fell.  So to me, the answer to the quandary (I think) is that Arizona's defense was not bad.  In fact, it was average for us or maybe even slightly above average. Cal's offense was outstanding, or the way I prefer to see it is that the Bears had luck on their side.  If the two teams have a rematch, I wouldn't be surprised to see a very different outcome.

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