*here, possession length = time until first action; see previous article for details.
A few years ago, Ken Pomeroy posted a plot of possession efficiency for each second of possession length, derived from five years of play-by-play stats for Division I college basketball. I re-posted that figure last time, so here I'll just show my re-plot of his data, along with possession efficiencies for three-second aggregate bins (0-3s, 3-6s, etc.) as I did last time for possession length:
For now, just focus on the solid gray line, which represents Ken's original data - I'll come back to the bins further down the page.
As Ken discussed in his original article, there are three areas of interest on the figure:
- For possession lengths less than 12 seconds, there is a large increase in scoring efficiency compared to possessions that last longer. There is a sharp peak at 3-4 seconds (typically fast breaks after steals) where the average D-I team is scoring better than 1.2 points per possession (ppp) - and remember that a middle-of-the-road team will likely average right at 1.0 ppp overall. However, the improved efficiency drops slowly from the peak, and finally reaches that 1.0 ppp baseline only at 12 seconds into the possession. Teams benefit greatly from scoring off the break, but continue to benefit well into the possession time as the defense scrambles to get set.
- For possession lengths of 12-30 seconds, there is very little variability in efficiency, as teams average 1.008 ± 0.010 ppp (yeah, I'm actually reporting a standard deviation here - get over it). There is a slight reward for scoring earlier in the possession: 12-24 seconds into the possession, teams average 1.013 ± 0.005 ppp, while 24-30 seconds into the possession the average drops to 0.996 ± 0.007 ppp. It's a subtle and not statistically significant difference. Here, we've effectively reached an even match between the offense and defense.
- For possession lengths greater than 30 seconds, efficiency decreases quickly with added time. As the last few seconds wind off the shot clock, scoring efficiency approaches 0.8 ppp, which is a very poor number. By now, the defense holds the advantage, as the offense loses its selectivity in an effort to get any sort of shot up at the basket.
So how did the Hoyas and their opponents fare compared to Ken's aggregate?
(more after the jump)