Given that the objective of NBA teams is to win (at least on the court), one would think that player evaluation would focus on that goal. When we look at the race for Rookie of the Year, though, it’s hard to see that focus.
The leading candidates for this award are Kevin Durant, Yi Jianlian, and Al Horford. Only one of these players, though, is playing for a team that has improved noticeably on last season’s results.
Last year the Sonics won 31 games with an efficiency differential (offensive efficiency minus defensive efficiency) of -3.0. This season the Sonics have a differential of -6.1. In sum, the Sonics with Durant are not as good.
The Milwaukee Bucks won 28 games last season with a differential of -4.6. This year the team’s differential is -5.2. In sum, the Bucks with Yi are not as good.
Turning to the Hawks, last season Atlanta won 30 games with a -5.1 differential. So far this season this team has a -0.5 differential. In sum, the Hawks with Horford are better.
My sense, though, is that both Yi and Durant are considered better rookies than Horford (at least, that’s how David Thorpe at ESPN sees it).
We could look at Wins Produced and see that this is not so, but let’s take a different approach. Kevin Durant replaced Ray Allen for the Sonics at shooting guard. Last year the Bucks employed a number of power forwards, but it appears Brian Skinner was the player most frequently employed at the position Yi currently occupies. And Horford has pretty much replaced Zaza Pachulia at center for the Hawks.
Imagine if these moves had not happened and the minutes currently allocated to the rookies were allocated to the players employed in 2006-07.
Part of the answer is revealed in Table One, where the per-48 minute performance of these six players – with respect to a variety of box score statistics — is compared to their position averages.
Allen for Durant
Let’s start with Durant and Allen. When we look at the individual stats we see that Durant has been well below average with respect to shooting efficiency. And although he’s above average with respect to blocked shots and rebounds, with respect to net possessions (rebounds + steals – turnovers) he’s again below average. When we turn to Win Score per 48 minutes [WS48] we see a mark of 4.4. Yes, that’s well below average as well.
In contrast, Ray Allen was quite good. No, he wasn’t very good with respect to net possessions. But his skills as a scorer far outweighed these deficiencies. Consequently his WS48 was above what we see from an average shooting guard.
When we turn to WP48 we see the same story. Durant has a mark of -0.010 thus far this season, which is well below average. Allen had a WP48 of 0.144, which is above the average value of 0.100. To put these numbers in perspective, with Durant this season the Sonics projected Wins Produced is 24.4. If the Sonics simply replaced Durant with Allen, and Allen posted the same numbers we saw in 2006-07, the Sonics projected Wins Produced would be 33.1. In sum, virtually the entire decline we see in Seattle is tied to Durant taking over for Allen at shooting guard (yes, the other moves practically make up for the loss of Rashard Lewis). And this is the player people think is the best rookie?
Skinner for Yi
When we turn to Yi, we see a similar story, although not quite so dramatic. Yi has shown an ability to avoid turnovers and blocked shots. With respect to everything else he’s below average. Consequently his WS48 is only 8.9 while his WP48 is 0.020.
Although Yi is below par, he’s productivity is not far below what we saw from Skinner last year. When we look at the numbers we might think Skinner should be above average. He was above average with respect to shooting efficiency and rebounds. But because he didn’t take many shots (yes, it turns out you do have to shoot once in awhile), his WS48 and WP48 marks were below average. Still, if Skinner – with a WP48 of 0.039 — took the place of Yi this season, the Bucks would be slightly improved. Of course, one suspects that a rookie has to out-perform Skinner to be considered Rookie of the Year.
Pachulia for Horford
The Hawks actually could run this experiment for us. Pachulia is still employed by the Hawks, although his starting position has been taken by Horford.
When we look at the numbers we see that Horford is above average with respect to rebounds and shooting efficiency. Although he has problems with respect to blocked shots, assists, and free throw percentage, his overall WS48 and WP48 marks (WP48 of 0.171) are above the mean.
Except for blocked shots, Pachulia was almost the opposite player last year. He had trouble hitting his shots and was below average on the boards. Given these problems, overall his WS48 and WP48 marks (WP48 of 0.096) were slightly below average. In sum, going from Pachulia to Horford improves the Hawks.
Summarizing the Story
When we look at the scenarios outlined in this column, we see that Durant and Yi have made their teams win less. Horford has made his team win more. And since winning is the objective, how is the current debate about the Rookie of the Year really much of a debate?
There are two issues to consider. One, people might be focused strictly on scoring. By that measure, Horford lags behind Yi and Durant.
Although the RoY debate in 2008 might be another example of scoring being over-emphasized, I think it’s also possible that people are addressing a different question. Rather than look at “how productive has a player been?” people might be considering “how productive will a player be in the future?”
At times Durant looks like a great player. Of course, the data tells us that there are many, many times he’s not. We expect as time goes by, Durant will be “great” more often and perhaps, he might even be more productive than Horford. A similar story could be told for Yi. Such stories might be what people consider when they argue that Durant and Yi are better rookies than Horford.
At this point, though, these are just stories. All we know so far is that the Hawks are better, and part of that improvement is tied to Horford. As for the Bucks and Sonics, each team has declined with the addition of their high profile rookie. And for the Sonics, the decline is quite dramatic. Durant, so far, has simply not helped Seattle win games. And although he might someday, the story today is quite different from these dreams about tomorrow.
Our research on the NBA was summarized HERE.
Wins Produced, Win Score, and PAWSmin are also discussed in the following posts:
Finally, A Guide to Evaluating Models contains useful hints on how to interpret and evaluate statistical models.