Posted Dec 9 2010 5:40PM
We've all heard the common sentiment around the NBA, the old one that teams with a lot of new faces -- like the Nets, Clippers and Timberwolves -- are probably banking on this season: "We need some time to gel. We'll get better as the season goes on."
On the surface, it makes sense. Success in the NBA comes with talent, but also with learning to play together. And teams that have turned over a big part of their roster probably do get better as the season goes on ... at least in an absolute sense.
But do they improve more than teams that bring back most of their players?
Looking at the last three years of data, the answer is no.
|Roster churn ...|
|Most roster turnover, 2010-11|
|... vs. roster stability|
|Least roster turnover, 2010-11|
|Ret. % = Percentage of minutes played by players on last years roster|
By comparing teams' efficiency differential (that is, the points scored per 100 possessions minus the points allowed per 100 possessions) at this point of the season with the efficiency differential at the end of the season over the last three years, we find that there's no correlation between in-season improvement and offseason roster turnover. (Roster turnover was measured by the percentage of a team's minutes that were played by players who were on the roster the previous season.)
There is a correlation between just how good teams are (both after 44 days and for a full season) and how little they turned their roster over. And that makes sense. Good teams aren't going to make many changes in the offseason, and they're going to continue to be good the following year. Success leads to stability and vice-versa.
But teams that get better as the season goes on don't really fit a profile. Some underwent change the previous summer. Some didn't.
Last season's Bulls were 6.8 points per 100 possessions better at the end of the season than they were after 44 days, which is a pretty incredible turnaround, the biggest of any team in the last three years. But 72 percent of the Bulls' minutes (more than the average of 69 percent) came from guys that were on the team the year before. The Bulls didn't necessarily gel. They just didn't play well to start the season.
Next most improved was the 2008-09 Thunder (+5.1 points per 100 possessions), who did have quite a bit of roster turnover. Russell Westbrook and Nenad Krstic were added to the young core that season and only 58 percent of their minutes were played by returnees.
But the year before, when the Thunder were still the Sonics, they had about the same amount of roster turnover (Kevin Durant and Jeff Green came in as rookies) and were a worse team at the end of the season than they were in mid-December.
The 2007-08 Sonics had a new coach, P.J. Carlesimo, to start the season. The 2008-09 Thunder made a coaching change, to Scott Brooks, in the middle of the season.
Like roster turnover, coaching changes provide a mixed bag of results. The 21 teams that made a coaching change in the offseason improved by just 0.1 points per 100 possessions from December to April.
The logic is that it takes time for players to get used to their new coach's system. And for the 2007-08 Rockets, with Rick Adelman in his first season in Houston, and the 2008-09 Bucks (Scott Skiles), that logic held water. The Rockets were 3.9 points better per 100 possessions at the end of the season than they were in December, and the Bucks were 3.7 points better.
But for the 2007-08 Grizzlies (Mark Iavaroni, -5.0) and 2009-10 Pistons (John Kuester, -3.5), there was some serious regression.
Teams that made a coaching change in the middle of a season have had better results, improving by 0.6 points per 100 possessions, with the Carlesimo-Brooks change being the prime example of a positive transition. It's said that it's easier to fire a coach than to fire the players. It might also be more effective, at least when it comes to in-season improvement.
Teams over the last three years that have undergone more than an average amount of summer roster turnover have actually regressed by an average of 0.2 points per 100 possessions from December to April.
This season, there's less of a correlation than normal between roster turnover and early success. Translation: More teams that made changes are pretty good. Obviously, this is a product of some high quality free agents taking their talents to new locations. The 14-9 Knicks had the third most roster turnover, the 15-8 Heat had the sixth most, and the 12-8 Bulls had the eighth most.
But we'll have to wait and see if those teams, as well the ones that haven't been as successful early on, are better in April than they are now. While it may make complete sense that teams that are new to each other will improve as they play more games, many of them don't.
This season's minutes are through Tuesday, Dec. 7.
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