Monday, November 12, 2012

Defense, Offense, and Pace: An Evaluation

A common lament about fast-paced, high-scoring teams is they have a ceiling; you can't win unless you focus on defense. But is there any truth behind team wins and pace? And does pushing the pace even help the offense?

Looking at seasons 1999-2000 to last season -- focusing on the post-Jordan (Bulls) era because it's a good a border as any and ignoring the weird lockout transitional season of 1999 -- there's a fairly sizable number of seasons with which to work. Pace is the number of possessions per game. Offensive efficiency is points scored per 100 possessions, and it's needed to compare the fast teams like the Nash-led Phoenix Suns of and Billups' snail-slow Pistons. Playing slow doesn't mean you're a bad offensive team. The same is true of defensive efficiency where people regularly conflate pace with ability as slow-paced teams are often called great defensively when they're mediocre, and this happens even with professionals analyzing basketball on TV. The Phoenix Suns never had a chance at being respected as a defensive unit because with their quick scoring the other team had more opportunities to score. But there is a further question of the correlation of defensive and offensive efficiency with pace, and the plots below explore this question.

The mess of dots is an indication of a weak association of defense and pace, if there's any association. The fastest paced team was Golden State in 2010, a crazy Don Nelson team that typically played without a center and scored 109 a game ... while giving up 112. The 2008 Nuggets were the second fastest, while the 2000 Kings ranked third. The Phoenix Suns, who are more notable for five of the seven best offensive seasons, rank behind teams like the 2008 Pacers or the 2000 Magic in pace. But the third best offensive season? The Roy-led 2009 Blazers, obviously. And as another surprise the Bobcats weren't even the worst offensive team: that label of honor belongs to the forgotten 2003 Nuggets, who had decent defense.

The slowest team is the Portland Blazers in 2004, which featured Zach Randolph and a traded-midseason Rasheed Wallace. The Pistons, however, were only sixth slowest, as the Jazz, Knicks, and Grizzlies beat them out. As for defense, the three best seasons all occurred in 2004 with the Duncan Spurs edging out the Wallace-brothers Pistons and the Artest Pacers. Perhaps a better method is to adjust efficiency for the season, but it's fine when looking at pace because the question is how teams respond when playing faster or slower. A pair of svelte shooting guards were featured on the two worst defensive teams: Kevin Martin and the 2009 Kings, and Ray Allen and the 2006 Sonics.

Putting the two components together in basketball-reference's SRS, which is basically how much you outscore another team adjusted for the strength of schedule, there's even less of an association. The outlier at the bottom is the 2012 Bobcats, arguably the worst team ever. What's amazing is that 397 out of 398 teams were between -11 and +9, and the Bobcats were 3.3 standard deviations from the mean. If we assume a normal distribution, the Bobcats are in the 0.05% percentile. You'd expect a team that bad out of every 2000 teams, which in a 30 team league is a once every 67 years event. They were truly historically bad. The strongest team by SRS? Strangely, the 2009 Cavs followed closely by the 2000 Lakers.

Plotting three variables at once in the figure below, there still doesn't appear to be any strong pattern with pace, defense, and offense. The color is used for pace where the fastest teams have the darkest color. Some of the ghostly points are hard to see with the background, but they're fewer in number anyway. What's important is the distribution of the dark points as they appear to be all over the place. Graphs are fine for data exploration, but an easy inquiry can be made into the correlation of both with pace via linear regression.

The results of the linear regression tests are in the table below. It appears that from 2000 to 2012, there's a statistically significant correlation between offensive efficiency and pace, where a higher pace equals a better offense, and the same is true with a stronger response with defense. But it is, however, not true with SRS, which is a strong proxy for wins. The coefficient was negative, but it's fairly small and the p-value is 0.15. This means there's a 15 percent chance there's no correlation of pace and SRS. The R^2 values indicate that very little of the variation in offensive and defensive efficiency is explained by pace; even though pace is significant the effect is quite small. An R^2 of 1 is ideal, meaning a perfect fit, and anything below 0.10 is very low. 

Offensive efficiency
Defensive efficiency

There's a small correlation of offense and defense with pace where the faster you play, the better your offense is and the worse your defense is. But overall, there's no proof a higher pace means you win less games. You can line up and slice the data in a multitude of ways, however; what's important is the interpretation. A correlation is simply a correlation. One explanation is that coaches who play faster prefer smaller players, and smaller players result in a poorer defense -- the Don Nelson effect. Pace could be correlated with another important explanatory variable. For example, business managers live longer than the average citizen, but that's because they make more money on average and have access to better health care. 

A further question is, does defense win championships? The average defensive efficiency of NBA champions since 2000 is +4.0, and the average offensive efficiency is only +2.6. Perhaps it's easier to win with defense because it's more consistent or they're able to control the offense of elite teams more than offensive teams are able to attack elite defenses. A study from Neil Paine of basketball-reference found that defense indeed is more important than offense in winning a championship, though not by a huge amount. Maybe a better study is seeing which teams outperform their regular season results in the playoffs, but that's a different study entirely. For now, there's a weak positive association of pace and offense, and a weak negative association of pace and defense. Point differential, i.e. win percentage? No pattern there -- teams that play fast don't appear to lose more often.

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