NBA players are known for their freakish size. Average height in the league has been six foot six or seven since the early 1960s, but the wingspan of NBA players is even more extraordinary than their height. According to David Epstein, the average person’s wingspan it slightly longer than their height, with a ratio of about 1.01:1. In the NBA, the average ratio is 1.05:1.
Some players have ratios much larger than this, allowing them to play bigger than their size. The average NBA shooting guard is 6’5, but Donovan Mitchell plays the position at 6’1. One factor that allows Mitchell to play above his height is his length. Michell’s 6’10 wingspan gives him a wingspan to height ratio of 1.12:1, well above the league average. This extra length helps him guard players who are taller than him, and may be a reason he averages about a steal and a half per game for his career.
It is common belief that wingspan directly impacts performance, especially on the defensive end of the floor. As a result, many teams prioritize filling their rosters with length, not just height.
But does wingspan actually have an impact on team defensive success? To find out, I calculated the average wingspan to height ratio for each team in the 2018-19 season. I used data from the NBA Draft Combine Anthrometric to find each team’s average ratio for the five players who played the most minutes last season. I then compared these averages to adjusted defensive rating (DRtg/A) from the 2018-19 season. I used DRtg/A because it is an estimate of points allowed per 100 possessions adjusted for strength of opponent offense.
After performing a linear regression of the data there does not appear to be a significant relationship between wingspan and team defensive success. According to the regression, team average wingspan to height ratio can only explain about 10 percent of the variation in DRtg/A. This finding could challenge the conventional belief that emphasizes the importance of wingspan, especially as a determinant of defensive prowess.
However, there does appear to be some correlation among the best defensive teams from last season. Out of the five longest teams from last year, three of them are among the top five for 2018-19 DRtg/A. This suggests that some elite defensive teams are exceptionally long, but length alone can’t make a team great defensively.
Although team wingspan may not be a good predictor of DRtg/A, it does have some impact on deflections. Of the top five teams in deflections last year, four were also in the top ten for wingspan to height ratio. Wingspan on its own can’t effectively predict a team’s defensive success, but perhaps taking into account other factors such as deflections, charges drawn, and coaching would provide a more accurate picture of defense in the NBA.