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October 8, 2008
NBA Trends
How the League is Playing the Game

by Kevin Pelton


"Past is prologue," Sen. Joe Biden said during last Thursday's Vice Presidential debate, quoting William Shakespeare. While that sentiment can be and was debated in terms of political policy, there is little question it is appropriate when it comes to statistical analysis. To know where the NBA is headed, we must first study what has happened in the past.

In this case, my interest lies not at the player or team level but in the league as a whole. Studied over time, league-wide statistics reveal some clear trends and some that are more opaque. Let's take a look.

We start with pace of play, something I addressed in an article early last season yet never revisited. At the time, the NBA was playing faster as a whole than at any time since the 1993-94 season. Things slowed thereafter, though possessions per game did increase for the second straight year and third in the last four, marking the fastest the NBA has played since the 1999-00 season (which was something of a historical outlier, as the following chart indicates).

Pace of play has jumped around quite a bit, in no small part because the league has attempted to speed up the game with various rule changes. Outside of these changes, the league has tended to consistently slow down. This is much more apparent when we look at a longer time period. Here's the league pace by year going back to 1977-78, the year of the ABA merger and what I consider the start of the modern NBA.

The NBA's moves have been as mundane as not resetting the shot clock all the way to 24 on fouls and as dramatic as allowing zone defenses. The most recent move, strictly enforcing the rules limiting handchecking on the perimeter starting in 2004-05, seems to have been the most successful. My suspicion is that the league will again play slightly faster in 2008-09, going from 91.0 possessions per 48 minutes to somewhere in the 91.3 or 91.4 range.

Besides the league's attempts to manipulate it, pace is also affected by coaching changes. None of this year's moves seems certain to cause a team to either slow down or speed up dramatically; most of the teams that changed coaches played in the middle of the pack in terms of pace, though Dallas (24th) and particularly Detroit (30th) were amongst the slowest teams (I'm ignoring Phoenix, since Mike D'Antoni stayed in the NBA). The Pistons have played at a glacial pace under three different coaches, and that seems unlikely to change now. One of those coaches was Larry Brown, who then coached a faster than average team during his one season in New York. Another was Rick Carlisle, now in Detroit, who was long one of the slowest coaches in the league before coaching a faster style his last two years in Indiana. So I'm not quite sure what to make of all of that.

While the rules reinterpretations may have helped speed up the game, their effect on offense league-wide has been much more apparent and much more dramatic. The last four years have seen a reversal of a decade-long trend toward less efficient scoring. Here's how it looks graphically.

In the late '70s and early '80s, offenses were getting better all the time, and quickly. (As for that downward spike in 1982-83, your guess is as good as mine.) Things then leveled off for about a decade. All of a sudden, whether because the Knicks' defensive tactics under Pat Riley caught on or because Michael Jordan retired, offenses collapsed in 1993-94.

The NBA answered by instituting the hand-check rules that would take center stage again more than a decade later, but the bigger change was moving the three-point line in to 22 feet. Predictably, three-point attempts jumped (more on that in a moment) and efficiency jumped up above previous levels to a record-high 109.7 points per 100 possessions. The bump, however, was temporary, and offense dropped again the next two years before the league thought better of the shorter line and removed it, causing another plunge.

The lockout produced the worst offensive basketball the NBA had seen since the first year after the merger, though the league jumped back the following year. In 2001, the league removed the illegal defense rule and allowed limited zones. Offenses improved slightly before the downward march resumed until the rules reinterpretations prior to the 2004-05 season produced a bigger increase than moving in the three-point line had. More importantly, the higher offensive efficiency has been sustained. Last year's 0.7-point increase in Offensive Rating pushed the league's scoring on a per-possession basis to its highest mark since 1995-96 and essentially to the same levels seen during the late '80s and early '90s.

As we look ahead to 2008-09, there is no obvious reason to expect the recent trend toward more efficient offense to reverse itself. League-wide efficiency could hit the 109.0 mark.

Digging deeper, there are interesting trends amongst the factors that help make up offensive efficiency. Free-throw attempts on a per-possession basis went up from approximately 11.9 percent of possessions ending in two-shot fouls in 2003-04 to 12.7 percent the following season because of the limitations on contact on the perimeter. However, by last year they had dropped back down to 12.0 percent of possessions, essentially the same as before. That seems to be a sign that the reinterpretation has had its desired effect, getting defenders to back off and allowing offensive players more freedom without drowning the game in a sea of whistles and trips to the charity stripe.

Turnover percentage per possession has bounced around without much rhyme or reason. After a surprising number of turnovers in 2006-07, the league became much more sure-handed a season ago, with 13.4 percent of possessions ending in turnovers, down from 14.2 percent the previous year. That 2007-08 rate was the lowest the league has ever seen.

One factor working against offense over time is a trend toward lower offensive rebounding percentages. This one is probably worth graphing.

The best offensive rebounding team in the NBA last season was the Philadelphia 76ers, who rebounded 31.8 percent of their own misses. That's a mark that, as recently as 14 seasons ago, would have been below average. The trend is towards teams sending more players back in transition defense and eschewing the offensive glass. Another minor factor is that three-pointers are slightly less likely to produce offensive rebounds than two-point shots (because second chances are so common in the paint) and that leads us to our final trend and one of my favorites, the amazingly consistent trend toward more three-point attempts.

I wrote extensively about the history of three-point attempts for 82games.com two years ago. If we adjust for the shorter three-point line and knock down the ratios for those three seasons, the trend since the early years of the three in the NBA is almost perfectly linear. The rate of increase has slowed very slightly of late, but the percentage of field-goal attempts from beyond the three-point line has still surpassed the short-line years. Last year, when 22.1 percent of all shots were threes, set a new record.

Though three-point percentage is not as consistent, it also continues to rise.

Last year saw NBA teams make at least 36 percent of their attempts from downtown (36.2 percent, to be exact) for the first time with the 23'9" three-point line.

The NBA's only elections are for the All-Star Game, and the Mavericks stick to Dallas, ignoring the White House. Still, in basketball as in politics, the one constant is change. 2008-09 should only continue that trend.

Kevin Pelton is an author of Basketball Prospectus. You can contact Kevin by clicking here or click here to see Kevin's other articles.

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Tough Calls (10/03)
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Change at the Top (10/10)

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