The first week of 2010 is the D-League's time to shine. The 16 teams of the NBA Development League have gathered in Boise along with NBA executives, including more than a half-dozen GMs, and writers for the annual D-League Showcase. The timing is appropriate because yesterday was the first day teams could sign players to 10-day contracts, making it easier to call them up from the D-League. Indeed, Idaho's Sundiata Gaines got the call from Utah Tuesday, making him the fourth player called up this season.
While much of the evaluation for potential D-League additions done by teams relies on first-hand scouting and tape, statistics play a role as well. However, D-League numbers come with a major asterisk because of the disparate level of play. As has been the case with college and European statistics, D-League performance may be easier to understand when it is translated to equivalent NBA numbers. So, using a similar method to the one used to create Basketball Prospectus' translations for draft-eligible players, I set out to create D-League translations.
The fact that the D-League is the one other league players regularly go back and forth from to the NBA in the same season is both a blessing and a curse in the translation process. It makes it possible to construct pure equivalencies without having to worry about the effect of aging, but also limits the sample size because call-ups and young players assigned to the D-League rarely see much time in the NBA that same season. Even players who do end up in large NBA roles often get called up early before they have a chance to put together much of a statistical line in the D-League.
Using a minimum of 250 minutes in both leagues, I found 15 players who qualified over the last three seasons: Alexis Ajinca, Kosta Koufos, Cartier Martin and Pops Mensah-Bonsu(2008-09); Nick Fazekas, Stephane Lasme, Steve Novak, Kasib Powell, Ramon Sessions and C.J. Watson (2007-08); Alan Anderson, Kelenna Azubuike, Andre Brown, C.J. Miles and Justin Williams (2006-07). Nine of the players were called up, while seven were assigned to the D-League by their NBA teams.
Using per-minute win percentage, here's what their performance looks like at the NBA level compared to the D-League.
While the relationship isn't exact--and Miles was amazingly awful in 2006-07 while playing for the Jazz--it is fairly linear. The r^2 of 0.29 suggests about 30 percent of the difference in these players' NBA production is explained by the difference in their effort at the D-League level, a number that isn't bad considering the small samples with which we are working.
The other big-picture takeaway is the amount of production that is lost going from the D-League to the NBA. On average, this is almost exactly 30 percent. I suspected there might be a greater drop-off for call-ups, who have more to play for in the D-League than players sent down by their teams, but the difference between them did not prove large enough to be significant. The bottom line is that an average player in the D-League (a .500 winning percentage) translates into a .350 winning percentage in the NBA, which is considerably below replacement level (about .415). 25 regular D-League players have played well enough that their translation is above replacement level. Given the uncertainty in the translations, that seems about right to me. By this standard, only a handful of players have been so good that teams could be reasonably certain that--based strictly on the stats--they would be useful contributors at the NBA level.
Here's how individual statistical categories translate from the D-League to the NBA.
The interesting thing here is that the biggest changes players experience have to do with external factors. In particular, when they get called up D-Leaguers go from being the stars to the little-known youngsters who get little respect from the referees. Lo and behold, their foul rates skyrocket, while they get to the free throw line far less often. At the same time, their role in the offense also diminishes dramatically.
One interesting note is that all those possessions that used to end in free throws don't turn into any extra two-point shots. Instead, players spend much more time beyond the arc in the NBA. Oddly, they don't become turnovers either, as players spend less time handling the basketball and actually commit fewer miscues.
Though this is all interesting from an academic perspective, the more practical aspect is how this applies to players currently in the D-League. Check back tomorrow as we look at the top D-Leaguers overall as well as the best available to teams looking for certain specific skills.
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Kevin Pelton is an author of Basketball Prospectus.
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