Can Players Improve Their Free Throw Shooting?
To me, this is by far the most important of these questions. It also happens to be the most difficult to answer with any sort of certainty from the data.
First, it's worth noting that there is a slight aging curve to free throw percentage. Players tend to improve by about 0.7 percent per season up through age 27 or so. The peak for free throw percentage is an extended one, as players don't really drop off consistently until age 32. Even then, the decline phase for free throw shooting is gradual. The other skills tend to give out long before free throw shooting, as illustrated by Bob Cousy's shooting in the movie Blue Chips.
Of course, when people talk about players improving their free throw shooting, that's not really what they mean. They're wondering instead why notoriously poor shooters like Dwight Howard and Shaquille O'Neal are unable to get in the gym and practice to improve their accuracy at the line. Consider me skeptical that such development is really possible for most players. Flipping around the perspective, most NBA players spend hours per week honing their shot at the line. Yet nearly all of them continue to shoot more or less the same percentage. It is possible that, beyond a certain point, additional practice simply no longer has any benefit.
To answer the question of whether practice helps at the line, I looked for pairs of seasons where the same player shot at least 100 free throws both years, then used statistics to evaluate how often the change in their percentage was larger than would be expected from random chance alone. As it turns out, players do seem intrinsically different at the line on a fairly regular basis--but this is true in both directions.
We would expect, based on the normal distribution, that 2.5 percent of players would either improve or decline by at least two standard deviations from one year to the next. In fact, nearly three times as many players made such a big jump (7.2 percent). But more than twice as many (5.5 percent) saw their shooting decay at the line. Free throw shooting, for whatever reason, is more random than chance would suggest.
There are more players taking sizeable leaps forward than backward, which suggests that practice is paying off for some players. However, the difference between the two groups is relatively small. We're talking about 90 players over the last three decades--about three per year. This is not something that is happening on a routine basis.
On the plus side, the players who made these improvements did tend to maintain them. The average player who improved by a statistically significant amount went from shooting 68.7 percent to 78.7 percent (precisely a 10-percent improvement) and shot 76.0 percent in year three.
A couple of superstar power forwards serve as the poster children for improving at the line. Chris Webber made the second-biggest leap in standardized terms, going from 45.4 percent during the lockout-shortened 1998-99 season (when free throw shooting was down around the league) to 75.1 percent in 1999-00. Webber had never previously made more than 60 percent of his free throws, but he only dropped below 70 percent once during the next seven seasons.
Karl Malone actually shows up on the list of most improved shooters in consecutive years. He went from making 48.1 percent of his free throws as a rookie to 70.0 percent in year three and only dipped below 70 once thereafter in his 19-year career, which he finished as the league's all-time leader in free throws.
The experience of Webber and Malone should serve to inspire players working tirelessly in the gym. At the same time, a handful of examples do not set reasonable expectations. In general, history tells us that players are who they are at the free throw line, which is worth remembering the next time you complain about missed free throws.