Monday, January 21, 2013

Contraction

The Sun Devils put up a decent fight until the last ten minutes or so.  It was as if their short bench finally got the best of them.  The Cats are definitely the deeper team, but what is interesting about our bench is that it is contracting.  On Saturday night, the bench played 55 minutes.  This was the 7th fewest minutes the bench has played all year.  The graph below shows the cumulative percentage of bench minutes played for the entire season.


In the early part of the season, as the rotation was forming, the bench was busy.  Against Long Beach State and Northern Arizona, bench players saw 86 and 83 minutes of time, respectively.  After the Texas Tech game, however, bench minutes started to contract.  The average game time the bench has seen has declined consistently over the last eight games.  The season average now stands around 65 minutes per game.  There is no doubt that this pattern is normal.  As coaches figure out what lineups work best, those lineups get increased playing time.   Nevertheless, I think it's worth asking whether leaning on the starters has led in this case to improved performance.  I'm not sure that it has.



First, let's look at defense.  The graph above shows the number of bench minutes versus the number points allowed per possession on the defensive end.  There is not much of a relationship here, and the one that is present is not statistically significant.  The overall pattern is that as bench players get more time, our defense gets better, but the relationship is so weak that we cannot be confident that it is real.  At best, we can conclude that our defense is unchanged regardless of how many minutes bench players see the floor.  What about offense?



The offensive numbers tell a similar tale but one that is more clear.   When the Cats go deeper into the bench, the offense scores more points, and this relationship is significant.  The only real outlier to this trend is the East Tennessee State game, where the bench had 91 minutes, but the offense only managed 1.0 points per possession.  According to our past performance, for every twenty minutes we get from the bench, the offense improves by approximately 0.1 points per possession, a meaningful difference.  In a typical game of 68 possessions,  this amounts to seven more points on the scoreboard.

One objection to this analysis might be that in blowouts, the offense runs very efficiently and the bench gets more minutes.  Therefore, this relationship might not be reflective of the Cats' offense as a whole.   If the same analysis is performed for games were the final point margin was equal to ten points or fewer, the same relationship holds, and in fact, it is even stronger.  Is it worth questioning whether bench minutes are moving in the wrong direction?  I'll leave that to the coaching staff.

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