Harvard Study: No Discernible Advantage to Fouling While Up Three

Posted by rtmsf on August 25th, 2010

One of the coolest sporting trends of the last decade in sports has been the increasing usage of statistical analysis to make determinations about the games that we love and follow.  While Bill James, Nate Silver and others have done yeoman’s work in popularizing the use of these metrics, they’ve mostly focused on the professional side of sports (and political polling, in Silver’s case).  One notable exception, Ken Pomeroy’s site of college basketball tempo-free statistics, has been invaluable in how we all understand and evaluate the game, helping to debunk common myths while also alerting us to teams and players under the radar of the national consciousness.  Another up-and-coming group that is showing it wants to enter the fray by analyzing some of the big questions in the game is the Harvard Sports Analysis Collective, who just two weeks ago presented us with the most unlikely finish of the 2009-10 season, a random game between Cal State Fullerton and Cal State Northridge.

Luckily the HSAC is a Little Better Than This (artist: B. Shabad)

Well, the HSAC is back, and today’s release is even better.  Addressing the widespread end-of-game question among announcers and pundits over whether a winning team should foul in late-game situations when up three points, the HSAC makes a rather curious finding.  It seems that over the past decade or so, there has been a slow but steady increase in the so-called conventional wisdom that fouling in those situations is the right play — the thinking being that the odds of the opponent making the first free throw, missing the second, and still securing the rebound and making another shot in a short period of time are very low.   That part is true.  The odds are low.  But what is equally low from a statistical standpoint are the odds of a strategy of simply playing defense and hoping you get the stop.  From the article:

In the 2009-2010 season, I found 443 instances where a team held the ball down three points during their last possession of a period (either the end of the 2nd half or an overtime period). In 391 of those cases, the team leading did not foul. In 52 cases, the team chose to foul. […]  Of the 52 teams that committed a foul, six lost the game for a winning percentage of 88.46%. Of the 391 teams that did not foul, 33 lost the game for a winning percentage of 91.56%.  Both a two sample t test of proportion and a Chi-squared test fail to reject the null hypothesis that there is a difference in winning percentage between the two strategies. In this sample, teams that did not foul won slightly more often.  For the less statistically inclined, this means that there is no significant difference between the two strategies. [emphasis added]

A few additional comments on this finding.

K-State Chose Not to Foul Jordan Crawford in the Sweet Sixteen

  • We were shocked that the defense decided to not foul in 391 of the 443 instances of this situation last year.  Shocked.  That means that 88% of the time, the defense stuck with the non-fouling strategy.  Given how often it’s discussed on television and elsewhere, we’d have figured it was closer to half the time.  An awful lot of virtual ink is written on the subject for something that occurs in practice only 12% of the time.
  • Even though there was no statistical difference in the strategies, we found it a little bit interesting that the fouling strategy ended up losing the game 3.12% more times last year.  Can you imagine a coaching staff reading that statement and (incorrectly) presuming that the no-foul strategy is clearly the right call?  In a sport where stressed-out coaches are looking for the tiniest of edges, we can actually envision that conversation happening at numerous campuses in the next few months.
  • The big fear of coaches who avoid fouling in these situations is that their player will foul someone on a three-point shot, giving up a possible four-point play that would lose the game.  It’s inconclusive how many of these instances were fouls gone wrong or just poor defense, but this situation only presented itself twelve times last year (and in nine of the cases, the fouled player made all three FTs).
  • Obviously, the data is only from one season (2009-10), but we wouldn’t expect that this year was significantly different than any other year.  It’ll be interesting to track, however, whether the HSAC mines the data from previous and future seasons to confirm this.

The author notes that this post isn’t the final chapter in this end-of-game analysis, which is stupendous news.  The next series of posts will analyze the effectiveness of using timeouts in various end-0f-game situations, and we’re thoroughly flush with anticipation to hear more of HSAC’s findings in coming weeks.

rtmsf (3998 Posts)

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5 responses to “Harvard Study: No Discernible Advantage to Fouling While Up Three”

  1. Brian says:

    I’ve never been a fan of fouling when up 3 but to me this study proves that both methods are effective. Of course when you’re up 3 with a few seconds left you have a very good chance of winning the game anyway.

    I was also surprised that not fouling was the overwhelming choice of coaches, considering how much this gets talked about in end of game situations.

  2. G. Floyd says:

    I would love to see the statistics when teams are down by 2, do they go for the win or tie. Do teams up by two foul a bad free throw shooter? If you are playing against Chandler Parson or Da’Sean Butler do you just accept a last second loss?

  3. Matt B. says:

    I think the percentage of teams choosing not to foul is a little misleading. The study was based on a teams last possession with a chance to tie. The HSAC readily admits in their comments that they were unable to use a time element because of a lack of standardization in NCAA play-by-play data. This means that games in which a player took a three to tie with 15 or 20 seconds left are treated the same as a buzzer beater if it was the trailing team’s last chance to tie the game with a single possession. I’m sure that if you limited the data to possessions that ended within the last 5 seconds, the percentage of games in which a team chose to foul would go up.

  4. Rudy says:

    Matt B is absolutely right. If there is no analysis of “when” the foul occurred, then this analysis tells us nothing.

    If you ask any coach this question – “If you’re up 3 on the last possession, do you foul”…the coach will answer your question with another question…”How much time is left?”

  5. jstevrtc says:

    The study claims that every game evaluated was in its LAST possession, meaning that, in most cases, there were at most 35 seconds left on the clock. Most likely there was less, since no coach would foul while up three with that much time left. Doing the study any other way wouldn’t make much sense (no coach in his right mind is going to foul intentionally if it’s not assumed to be the last possession of the team that’s down three), so the ability to generalize is there. If you ask a coach that question, and they say, “How much time is left?” I think I’d reiterate the fact that it’s the last possession. Even if there’s 1:30 left, and one or more offensive rebounds happens, you can count on the fact that the coaches fouled intentionally at an “appropriate” time. Of COURSE a coach is less likely to foul with 20 or so seconds left. That’d be idiotic.

    I would wager that if the HSAC went back and checked when most of the intentional fouls occurred, it’d be with less than ten seconds left, and many of the examples would be with even less than that. If you want only data that includes intentional fouls in the last five seconds, I think it’s a reasonable assumption that that’s exactly what you’re getting, because to foul with MORE time is so much riskier. The study is retrospective, meaning it’s based on real-world events that happened in the past, so you’re not going to get a skewed sample where all these coaches are fouling intentionally with, say, 30 seconds left. Yes, the HSAC should have included that information in their writeup. But I think this is much less of an issue than a few people are making because coaches just aren’t going intentionally foul up three points unless it’s the right thing to do, considering how much time is left. There are only, what 52 occurrences in the sample? How many coaches out of that 52 do you think intentionally fouled with a LOT of time left?

    John from RTC

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