You gotta love percentages…they’re just so versatile. You start with perfection (100%) and work from there. In basketball, we’re all familiar with the basic percentage-based stats like field goal percentage and in earlier installments of this series I covered some trickier ones like effective field goal percentage and true shooting percentage. However, there are a whole series of other percentage-based basketball stats that are used to evaluate individual performance on the court. All but one (usage%) are simply a different way to evaluate specific aspects of basketball performance that already have familiar measurement stats. None are particularly revolutionary, but since they’re increasingly being used by the hoops media, we’ll take a quick look at them.
Usage Percentage
Usage% is the one percentage-based statistic that isn’t simply a percentage-ized version of a familiar stat. I could give show the formula, but I’ll try describing it in plain English and give the masochists a link:
http://www.basketball-reference.com/about/glossary.html
Usage percentage takes an individual player’s total number of shots, free throw attempts and turnovers and compares this to the total number of shots, free throw attempts and turnovers of the team during the minutes the player is on the floor. Since every offensive possession ends with either a shot, free throw attempt or turnover, one way of looking at usage% is, relative to minutes played, how often does a player have the ball when a possession ends.
On a perfectly-balanced team, each player would have a 20% usage% (100% divided among the 5 players on the floor). The current Celtics team comes about as close to this as any NBA team, with no player having a usage% over 25%. Not surprisingly, when you look at the league leaders in usage, you’ll find most of the league’s scoring leaders:
Kobe Bryant (Lakers) – 34.5%
Carmelo Anthony (Knicks) – 32.5%
Derrick Rose (Bulls) – 32.2%
Dwayne Wade (Heat) – 32.0%
Russell Westbrook (Thunder) – 31.7%
It’s interesting that the league’s leading scorer, Kevin Durant of the Thunder (28.1 points per game – usage 30.7%) not only isn’t among the league leaders in usage, but isn’t even the highest usage player on his own team. It’s then not surprising that Durant is one of the most efficient high-volume scorers in the league with a 59.2% True Shooting Percentage.
Looking for a high usage player who doesn’t deliver? Well, Mo Williams (now on the Clippers but who played mostly for the Cavaliers this season) has a fairly high 25.9% usage% but has only managed to score 14ppg this season…not good.
Traditional Stats “Percentage-ized”
Statisticians have been keeping track of rebounds (offensive, defensive and total), assists, blocks, steals and turnovers for a long time, the newest being turnovers which came into the stats world for the 1977-78 NBA season. You take the basic stat, divide by the number of games and get the familiar per game statistics we use to compare players.
Most of us know that 10 rebounds per game (rpg) sort of defines an excellent rebounder. Nearly all who approach this standard either play center of power forward. A small forward who grabs 7 rpg is very good as are shooting guards who pull down 5rpg and point guards who snatch 4rpg. For assists, 7+ per game (apg) is good for a point guard…4 apg is very good for other positions. Blocks pretty much are only meaningful for “bigs” (centers and power forwards)…unless your name is Lebron James. If you average 2+ blocks per game (bpg), you’re among the league leaders. Steals are sort of the balance to blocks, since little guys tend to dominate this stat, and like blocks, 2+ steals per game (spg) defines elite status. Turnovers are the only “bad stat” that’s kept on a per game basis. You’d think that point guards who handle and pass the ball the most would routinely lead in turnovers per game (topg), but it’s actually a fairly democratic stat. In general, players with high usage percentages and play a lot of minutes, are among the league leaders (3+ topg).
So why create percentage versions of these traditional stats? A couple reasons. First and foremost, using only a per game basis gives you no insight into the relative performance of players who don’t play big minutes. For example, the Bulls backup center, rookie Omer Asik, is averaging 4.0 rpg…not very impressive for a 7-footer. However, he only averages 12 minutes played per game (mpg) so his 4 boards begins to sound a little better. There are two ways to level the playing field for low-minutes players. One is to use percentages and the other is to use some sort of per-minute basis. The most common of the latter are to convert the stats to a “per 36,” “per 40” or “per 48” (full regulation game) minute basis. Personally, I like the “per 36” stats since that’s a fairly normal number of minutes for a starter. On a per-36 minutes basis, Asik’s 4.0 rpg translates into a pretty stellar 11.9 rebounds per 36.
The “percentage-ized” traditional stats not only adjust for minutes played, but for everything else as well. For example, if a team makes an unusually high percentage of their shots, there are fewer offensive rebounds to be had. A horrible defensive team doesn’t have that many defensive rebounding opportunities because their opponents make everything they look at. All things being equal, a team that plays at a fast pace provides more opportunities for every stat because there are more possessions per game. Percentages remove all that noise.
So yeah, it may seem like taking the traditional stats and turning them into percentages is a case of the stats guys playing with themselves, there is actually a method to their madness. We’ll take a look at these, but since they all use the same basic methodology, we’ll only go through the math for total rebounding percentage (TRB%).
The formula for TRB% is:
100 * (TRB * (Team Minutes Played / 5)) / (Minutes Played * (Team TRB + Opponent TRB))
OK, stay with me now. The 100 is in there to make the end result a percentage, so let’s not worry about that right now. Team Minutes Played / 5 is simply the total number of minutes played by any one of the 5 positions on a team. TRB is the total rebounds for the player we’re measuring. Minutes Played is the total number of minutes played by the player we’re measuring. When you add Team TRB and Opponent TRB you get all the rebounds that have been grabbed in your games.
Let’s do an example that also performs the perfection test. To do this, we need to use the completely unrealistic situation where in 10 regulation games (no overtimes) a player played all of the 480 minutes possible and while he was in there, he snatched all of his team’s 500 rebounds. Since we’re dealing with perfection, his opponents’ had no rebounds:
500 * 480 / 480 * 500 = 1.00 or when multiplied by the 100 in the formula, 100%
It’s not surprising that the leaders in rebounding percentage also are near the top in terms of rebounds per game. This is because true rebounding studs tend to play a lot. Here are the current rebounding leaders:
Kevin Love (Timberwolves) – 1st in rebounds per game (15.6) and third in TRB% (23.7%)
Dwight Howard (Magic) – 2nd in rebounds per game (14.2) and tied for 4th in TRB% (21.9%)
Zach Randolph (Grizzlies) – 3rd in rebounds per game (12.6) and 7th in TRB% (20.5%)
Blake Griffin (Clippers) and Pau Gasol (Lakers) round out the top-5 in terms of rebounds per game, but neither cracks the top-10 for TRB%. Reggie Evans of the Raptors leads the NBA with a TRB% of 26.6% and the Trailblazers’ veteran Marcus Camby is second at 24.2%.
So when it comes to TRB% anything in the high teens is very good and 20%+ is truly elite.
Assist percentage (AST%) is an estimate of the percentage of teammate field goals a player assisted while he was on on the floor. The current leaders in AST% are the Celtics’ Rajon Rondo (45.5%), the Mavericks’ Jason Kidd (45.1%), the Raptors’ Jose Calderon (43.5%), the Suns’ Steve Nash (40.9%) and Earl Watson of the Jazz (39.2%). All but Watson are also among the NBA leaders in assists per game. Watson only averages 3.3 assists per game in 17.5 minutes per game, so he clearly benefits from the percentage version of the assist stat.
Block percentage (BLK%) is an estimate of the percentage of opponent two-point field goal attempts blocked by the player while he was on the floor. The current leaders in block percentage are the Wizards’ JaVale McGee (6.8%), the Timberwolves’ Darko Milicic (6.7%), the Thunder’s Serge Ibaka (6.4%), the Bucks’ Andrew Bogut (6.0%) and Joel Anthony of the Heat (5.5%). These 5 players are also the top 5 in terms of blocks per game, ranging from Milicic’s 2.16 blocks per game to Bogut’s league-leading 2.87 blocks per game.
Steal Percentage (STL%) is an estimate of the percentage of opponent possessions that end with a steal by the player while he was on the floor. The current leaders in steal percentage are the Grizzlies’ Tony Allen (4.8%), the Hornets’ Chris Paul (3.7%), Rondo (3.3%), the Warriors’ Monta Ellis (2.8%) and Manu Ginobili of the Spurs (2.7%). Allen, Paul, Rondo and Ellis are also in the top 6 for steals per game, ranging from Allen’s 1.74 steals per game to Paul’s NBA-best 2.46 steals per game. Ginobili ranks 13th in the league with 1.61 steals per game, so the percentage-ized stat gives the clearer indication of his prowess at defensive thievery.
Turnover percentage (TO%) is an estimate of turnovers per 100 plays. The current “leaders” in this negative stat are the Bobcats’ Joel Przybilla (29.6%), the Hawk’s Hilton Armstrong (21.9%), the Bulls’ Asik (21.3%), the Magic’s Chris Duhon (21.2%) and the Raptor’s Joey Dorsey (21.0). Przybilla and Asik are centers. Armstrong is a forward-center, Duhon is a point guard and Dorsey a wing-forward…like I said, turnovers are a pretty democratic stat. Another unusual thing about the TO% stat is that none of the leaders in TO% are among the league leaders in turnovers per game. There’s a simple reason for this…if you commit turnovers at an exceptionally high rate, coaches aren’t going to play you very much. None of the top-5 in TO% are regular starters.
The best and easiest place I know of to get these “percentage-ized” stats is basketball-reference.com. It’s a great site if you want to go past the basic stuff and get a little geeky. Another good source is stats Guru John Hollinger’s Insider site at espn.com.
Next up: advanced team stats.
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