Player: Defense and Rebounding
The "Defense and Rebounding" table has some advanced versions of the basic defense and rebounding stats: BLK%, STL%, FOUL%, fgOR%, fgDR%, ftOR%, ftDR%. Let's go through them in order. Unfortunately defense and rebounding is an area where we'd do better with more advanced stats. These are poor representations of a player's defense and rebounding ability — we're often better off looking at team level impacts than these stats alone. But they do have some useful (even if basic) information.
BLK%click to show/hide
Block percentage measures how often the player blocked a shot when an opponent was attempting one.
Example: Giannis Antetokounmpo
Giannis has been a very good shot blocker for his position his whole career. He took a leap in his third year, and has blocked more than 2% of opponent shots while on the court since that point.
The Gritty Details
CTG calculates block percentage by dividing a player's blocks by the opposing shot attempts while they are on the court. Shot attempts include all field goals plus shooting fouls drawn (avoiding double counting and-ones). Note that other places you see block percentage sometimes only look at blocks per opposing two-point attempt, and most others do not include opposing fouls drawn in the shot attempts.
STL%click to show/hide
Steal percentage measures how often the player got a steal per play he was on defense. A STL% of 2.0% means that for every 100 defensive plays, the player got 2 steals.
Example: Giannis Antetokounmpo
Giannis' steal rate was around average for his first few years, but took a big jump in his fourth season. It dipped this last year, as Mike Budenholzer changed the Bucks' defense to a less aggressive style.
The Gritty Details
CTG calculates steal percentage by dividing a player's steals by the defensive plays he was on the court for. A defensive play is a field goal attempt, turnover, or trip to the foul line. Note that other places you see steal percentage often do steals per defensive possession, rather than per defensive play. The differences in these shouldn't be large, but that is why the numbers might not match up.
FOUL%click to show/hide
Foul percentage measures how often the player committed a defensive foul. It's important to note that fouling more is not always bad. In fact, there are often players who foul very little who are quite poor defenders — the fact that they don't foul is a sign that they're not active or aggressive enough defensively. (Jamal Crawford is a great example of this. Through his career he's been an extremely low foul player, but his teams have generally been much worse defensively when he plays than when he sits. And in fact, despite Crawford's low foul rate, his teams have also tended to foul much more when he plays.)
Example: Giannis Antetokounmpo
Giannis was never particularly foul prone, though he has lowered his rate of fouls over the course of his career while still maintaining those high block and steal rates.
The Gritty Details
CTG calculates foul percentage by dividing a player's fouls committed (taking out offensive fouls) by the defensive plays he was on the court for. A defensive play is a field goal attempt, turnover, or trip to the foul line.
Rebounding percentages: fgOR%, fgDR%, ftOR%, ftDR%click to show/hide
The only time a player can get a rebound is on a missed field goal or a missed free throw which is the last of a set of free throws. So when we measure how good a player is as a rebounder, we have to take into account how many opportunities he had to get one. Otherwise a player who plays for a team that forces a lot of misses might seem to be a better rebounder than he is. It's not necessarily that he got more rebounds, it's that there were more misses when he was on the court!
That's what these rebounding percentages measure: how often a player got a rebound per opportunity he had to get one. These stats separate out offensive rebounds ("OR") from defensive rebounds ("DR") and missed field goals ("fg") from missed free throws ("ft"). These are all very different rebounding situations, so we should look at them differently. Field goal misses happen much more frequently and are more contested, and therefore when looking at rebounding you should predominantly look at the fgOR% and fgDR% columns.
Example: Giannis Antetokounmpo
Giannis has become a better rebounder over his career, in part because he's played more PF and less SF as his career has gone on. That said, he took a big leap in defensive rebounding in 2018-19, to have the highest rate of defensive rebounding of any forward in the league. Interestingly, Giannis has also become a much better free throw rebounder in recent years. On the defensive end this might just be him chasing stats, but he also rebounded a high rate of missed free throws on the offensive end in 2018-19.
The Gritty Details
CTG calculates rebounding percentages by actually measuring how many misses occur in each category when the player is on the court, and dividing the player's rebounds of each type by his opportunities of each type.