March 15, 2012 - by Jeff Haley
***IMPORTANT NOTE*** This is an entry in our inaugural Stat Geek Idol contest. The opinions and predictions expressed below do not represent the views of TeamRankings.com, and are solely those of the author. This article was conceived of and written by Jeff Haley of hoop-math.com.
During coach Bo Ryan’s tenure, the Wisconsin Badgers have consistently been among the best defensive teams in all of college basketball. This season, the Badger defense is particularly strong heading into the NCAA tournament, ranked #4 overall by Ken Pomeroy. The Badgers are #2 in the country with an opponent’s effective field goal percentage of 41.8%.
So what makes Wisconsin so difficult to score on?
Play-by-play statistics provide a powerful tool to answer these sorts of questions. Using publicly available play-by-play game logs, we can classify each attempted shot into three broad categories.
Three point shots are grouped into one category. The second category — shots attempted at the rim — includes layups, dunks, and tip shots off of offensive rebounds. The remaining two point shots are classified as two point jump shots.
To get a better feel for what the shooting percentages are for various types of shots, and the frequency with which each shot type is attempted, we can look at the 2011-2012 season average for major conference teams.
About one third of shots were at the rim, about one third were two point jump shots, and about one third were three point jump shots. (The exact breakdown is listed in a table below.) Teams on average make 64% of their shots at the rim, 35% of two point jump shots, and 34% of three point jump shots.
Adding up all of these contributions, a hypothetical team with an average shot distribution and shooting percentages would have an effective field goal percentage of just under 50.0%.
The table below compares the shot distributions and percentages that Wisconsin has allowed this season with the typical offensive shot distributions and percentages of major conference teams.
The first column of the table contains the average results for major conference teams when on offense (labeled “Major Conference Average”). The second column shows the percentages that Wisconsin has allowed defensively (labeled “What Wisconsin Has Allowed”). We see that overall, Wisconsin’s opponents have typically shot a lower than usual field goal percentage at the rim, shot a lower percentage from three point range than is typical, and have shot far more two point jump shots and far fewer three point jump shots than what we normally see in college basketball.
The table also lists how Wisconsin’s major conference opponents fared against the Badger defense, which is shown in the third column of the table (labeled “Major Conference Teams vs. Wisconsin”). The results against major conference teams are similar to the results when we look at Wisconsin’s entire set of opponents. The Badger’s low opponent effective field goal percentage comes from a combination of low opponent field goal percentages at the rim and from three point range, and a low rate of opponent three point attempts.
The fourth column in this table shows the season averages for these categories for Wisconsin’s major conference opponents (labeled “Major Conference Opponent Averages”). The average shooting percentages and shot distributions of Wisconsin’s major conference opponents were not meaningfully different from a typical major conference team. It stands to reason that Wisconsin’s low opponent effective field goal percentage is not the result of playing against weak offenses.
Let’s take a deeper look at the three things that reduce Wisconsin’s opponent effective field goal percentage.
1. FG% at the rim. Opponents make 52% of their attempts at the rim against the Badgers. The major conference average for this statistic is 64%. The difference between 52% and 64% shooting on attempts at the rim changes effective field goal percentage by about 4%. Part of Wisconsin’s success at lowering opponent’s shooting percentage at the rim comes from their ability to block shots. Wisconsin is far from the best shot blocking team in the country, but they do manage to block 13% of their opponent’s attempts at the rim. Wisconsin’s opponents make about 59% of their shots at the rim on unblocked shots. This is still a pretty low total, which hints that Wisconsin is doing things beyond blocking shots to reduce opponent’s shooting percentage at the rim.
2. Three point shooting percentage. Wisconsin’s opponents shoot only 28% from three point range. The difference between 28% and the major conference average of 34% amounts to a difference in effective field goal percentage of a bit less than 4% for a team that allows the shot distribution that Wisconsin allows. Recent work by Ken Pomeroy suggests that it is potentially hazardous to read too much into opponent three point shooting percentage. With so few three point attempts being taken, there can be a lot of noise in the data. Noise or not, this low three point percentage is a significant factor in producing the low effective field goal percentage of Wisconsin opponents.
3. % of FGA taken from three point range. Wisconsin’s opponents have taken only 24% of their field goal attempts from three point range this season, compared with the division one average of 34%. As a result of this, Wisconsin’s opponents end up shooting two point jump shots on 43% of their attempts. Running shooters off the three point line is always a good play for the defense. Most college basketball teams shoot pretty similar percentages on two point jump shots and three point jump shots; the major conference average shooting percentages on these two types of shots are almost the same. By reducing opponent three point attempts in the way that they do, Wisconsin shaves about 1% off of their effective field goal percentage.
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