Posted by Neil Paine on February 6, 2009
It can be confusing to keep up with some of the statistical terms and abbreviations I frequently use here at the BBR Blog, especially in the rare cases where the definitions I prefer to use differ from those found in our lovely Glossary. That's why I thought it would be a good idea to spell out exactly what I mean when I refer to certain terms and use certain abbreviations...
%FGA: % of Team Shots = 100 * FGA / ((MP / (Tm MP / 5)) * Tm FGA). An estimate of the % of team shots that a player takes while on the court. %FGA is essentially a shorthand form of %Poss that's a lot easier to calculate, the drawback being that it only includes shots (and not assists, offensive rebounds, etc.).
%Poss: Possession % = 100 * Poss / ((MP / (Tm MP / 5)) * Tm Poss). Possession percentage (sometimes referred to as "usage %") estimates the % of team possessions a player consumes while on the floor. Along with ORtg, it is an essential component of assessing a player's offensive effectiveness and his role on the team. It is also important when building "skill curves" and plotting usage vs. efficiency.
2P%: 2-point FG% = (FG - 3P) / (FGA - 3PA).
3p%: 3-point FG% = 3P / 3PA.
3Ptd: 3-point Tendency = 3PA / FGA. A measure of what % of a player's shots come from long-distance.
AsR: Assist Rate = 100 * AST / (((MP / (Tm MP / 5)) * Tm FG) - FG). Assist rate estimates the percentage of teammates' baskets a player assisted on while he was on on the court.
Blk%: Block Percentage = 100 * (BLK * (Tm MP / 5)) / (MP * (Opp FGA - Opp 3PA)). Block percentage is an estimate of the percentage of opponent two-point field goal attempts blocked by the player while he was on the floor.
DPA: Defensive Points Added. An estimation of the # of points/100 poss. saved by the player vs. an average player. See this post for further explanation.
DR%: Defensive Rebounding Percentage = 100 * (DRB * (Tm MP / 5)) / (MP * (Tm DRB + Opp ORB)). Defensive rebounding % is an estimate of the percentage of the opponent's missed shots a player grabbed while he was on the floor.
DRtg: Defensive Rating = 100 * (points allowed / individual def. posessions). An individual is assumed to individually face 20% of opposing possessions while on the floor, and his DRtg on these possessions is a product of his Stop%, or 1 - the Floor% of the opponent he's facing. Stop% is determined by the player's rate of creating stops (forced turnovers, forced misses, defensive rebounds, steals, & blocks). The player's DRtg on the other 80% of possessions is assumed to be his team's base defensive rating on plays he didn't stop directly, since defense is far more of a team-oriented activity than offense is.
DWS: Defensive Win Shares.
eFG%: Effective Field Goal Percentage = (FG + 0.5 * 3P) / FGA. This statistic adjusts for the fact that a 3-point field goal is worth one more point than a 2-point field goal. For example, suppose Player A goes 4 for 10 with 2 threes, while Player B goes 5 for 10 with 0 threes. Each player would have 10 points from field goals, and thus would have the same effective field goal percentage (50%).
GmSc: Game Score = PTS + 0.4 * FG - 0.7 * FGA - 0.4*(FTA - FT) + 0.7 * ORB + 0.3 * DRB + STL + 0.7 * AST + 0.7 * BLK - 0.4 * PF - TOV. Game Score was created by John Hollinger to give a rough measure of a player's productivity for a single game. The scale is similar to that of points scored (i.e., 40 is an outstanding performance, 10 is an average performance, etc.).
Floor%: Floor Percentage = Individual scoring possessions / individual possessions used. Floor % answers the question, "when Player X uses a possession, what is the probability that his team scores at least 1 point?" Differences in quality between a player's Floor% and ORtg are frequently due to the 3-point shot. For instance, a big man who never takes threes may have a lower ORtg but a higher Floor% than a 3-point specialist. That's because the 3-pointer is often volatile -- high risk, high reward -- while the probability of the big man's inside attempts resulting in points stays relatively constant -- there's less reward (2 points instead of 3), but also less risk involved.
FTr: Free Throw Rate = 100 * (FTA / FGA). Free throw rate is the ratio of free throws attempted per field goal attempted. It's useful to assess where the bulk of a player's shots are coming from -- low ratios usually indicate a lot of jump shots (fouls are less prevalent the further away from the basket you get), while high rates are the province of inside players who often take strong shots in traffic down low. A variation on FTr is Bob Bellotti's old Rice-Scott Index (RSI), which is just FGA / (FGA + FTA) (so named because when the stat was developed, long-range bombers Glen Rice and Dennis Scott had extremely high RSIs).
OR%: Offensive Rebounding Percentage = 100 * (ORB * (Tm MP / 5)) / (MP * (Tm ORB + Opp DRB)). Offensive rebounding % is an estimate of the percentage of available offensive rebounds a player grabbed while he was on the floor.
ORtg: Offensive Rating = Individual points produced / individual possessions used. Along with %Poss, ORtg is vital to assessing a player's offensive productivity. Because it effectively combines TS%, OR%, AsR, and ToR into one metric, it is the ultimate measure of a player's offensive efficiency. That's not to say every player with a high ORtg is better than ones with lower ORtgs, though (see skill curves).
OWS: Offensive Win Shares.
P/36: Points per 36 minutes = 36 * Pts / MP. I also adjust this stat for pace by multiplying points by (Lg Poss per 48 min / Tm Poss per 48 min).
Poss: Individual Possessions. Used when a player ends his team's possession, either by attempting a free throw or a field goal, grabbing an offensive rebound, making an assist, or committing a turnover (for the gory details on calculation, see Basketball on Paper).
PPR: Pure Point Rating = 100 * (Lg Poss per 48 min / Tm Poss per 48 min) * (((AST * 2/3) - TOV) / MP). Developed by John Hollinger, PPR is a better "ballhandling" metric than regular assist-to-turnover ratio because it properly weights assists & turnovers relative to each other, and it presents the two in a per-minute form.
PProd: Points Produced. The are points generated by an individual, whether by a made FG, a made FT, an offensive rebound, or an assist. Again, see Basketball on Paper for the details on calculation.
qAst: The percentage of a player's FG that are assisted, as estimated by his assist rate and eFG%, among other stats.
Skill Curves: Since 100% of team possessions must be used by the offense at all times -- and there is an inverse relationship between %Poss & ORtg -- there is a lot of "extra" offensive value (beyond a player's ORtg, that is) in simply creating shots and using those possessions. This is the idea behind what Dean Oliver called "skill curves" in Basketball on Paper... Basically, as a player's role in the offense increases, his efficiency will go down because he's having to take shots of increasing difficulty; at the same time, he's boosting his teammates' ORtgs because they don't have to take those tough shots anymore. This is why someone like Michael Jordan was so valuable -- he was able to maintain an ORtg of 120-125 even while assuming 30-35% of the Bulls' possessions when on the court, which in turn diverted defensive attention away from his teammates and created easier chances for them as well. So here are some rules of thumb: Players who have both a high ORtg (>110) and a high %Poss (>23) are offensive stars; players with a high ORtg and a low %Poss (<17) are good role players who may be able to take on more possessions and still maintain a reasonable efficiency level; players who have a low ORtg (<104) and a high %Poss are probably not suited well for their role and need to shoot less; finally, players with low marks in both categories are either defensive specialists or scrubs.
SPM: Statistical Plus/Minus. An estimation of the player's Adjusted +/- score, using his boxscore stats and his team's point differential. See this post for a more detailed explanation.
Stl%: Steal Percentage = 100 * (STL * (Tm MP / 5)) / (MP * Opp Poss). Steal Percentage is an estimate of the percentage of opponent possessions that end with a steal by the player while he was on the floor.
Stop%: Stop Percentage = (Stops * Tm MP) / (Tm Poss * MP). The % of opponent individual possessions directly stopped by a player through steals, blocks, forced misses, defensive rebounds, and forced TO. This assumes a player faces 20% of opponent possessions when on the floor; on the one hand this is patently untrue, but on the other hand defense is more of a team-oriented activity anyway. This is the roughest estimate out of all of the advanced stats here.
ToR: Turnover Rate = 100 * (TOV / Poss). The percentage of a player's individual possessions that end in a turnover.
Touches: Touches = FGA + TOV + (FTA / (Tm FTA / Opp PF)) + (AST/0.17). Developed by Bob Chaikin, touches estimate the number of times a player touched the ball in an attacking position on the floor. The theory behind the formula is that once a player gets the ball, he can only do one of four things (aside from dribbling, of course): pass, shoot, draw a foul, or commit a turnover.
- T/Min: Touches per minute. I also adjust this stat for pace by multiplying touches by (Lg Poss per 48 min / Tm Poss per 48 min).
- %Pass: %Pass = 100 * (AST / 0.17) / Touches. The percentage of a player's touches that ended with him passing to a teammate in an attacking position on the floor.
- %Shoot: %Shoot = 100 * FGA / Touches. The percentage of a player's touches that ended with him taking a shot and not being fouled in the act.
- %Fouled: %Fouled = 100 * (FTA / (Tm FTA / Opp PF)) / Touches. The percentage of a player's touches that ended with him drawing a foul.
- %TO: %TO = 100 * TOV / Touches. The percentage of a player's touches that ended with him turning the ball over.
TS%: True Shooting Percentage = PTS / (2 * (FGA + 0.44 * FTA)). True shooting percentage is a better measure of shooting efficiency than FG%/FT%/3P%, because it takes into account all three component percentages, plus FTr.
Translated Stats: Efficiency stats (ORtg and DRtg) that have been translated into a different league context, much like you would use exchange rates to change currency. See this post for a more detailed explanation.
WS: Win Shares (see Calculating Win Shares for the details on calculation).