Quote tkfu wrote: View Post
Yeah. The reason possessions are defined like that is basically because it's more useful to think that way. As you said, if we defined possessions the way you suggest, teams would have different numbers of possessions each game. That would make per-possession efficiency numbers useless until you added in the possessions-per-game stat.

It's usually more revealing, when you're looking at team-level stats, to have a measure for overall efficiency. You can them break that down into its component pieces if you want to drill down and see why the efficiency is what it is. So you see your team has an overall offensive efficiency of, say, 100.0 pts per 100 possession. That's a good measure for comparing how good your offense is overall compared to other teams. But now you want to see what is helping you and what's hurting you, so you check what percentage of possessions end in turnovers, or assists. If you want to know about rebounding, you check to see what percentage of available rebounds your team got, breaking it down into off/def if you want. If you want to know about scoring efficiency, you look at TS%.

Regarding your four points above:

1 & 2: Well yeah, it would be different. But it wouldn't be better, because all you've changed is removing offensive rebounds. You'd have a stat called "possessions" whose only function would be to tell you about rebound differential. We already have that stat, it's called rebound differential. We also already have a stat for scoring efficiency, TS%. And if, for some reason, you really wanted a stat for offensive or defensive efficiency that included turnovers but not rebounding, well, the math is easy enough without redefining the meaning of "possession". Another side-effect of your proposed change would be that any time you wanted to look at per-possession numbers as a measure of efficiency, which is what we use per-possession numbers for most of the time, you'd have to adjust them for rebound rate. It just doesn't make sense.

3 & 4: No, how a possession is defined on the team level wouldn't have any effect on how an individual player is valued. Any box score-based stat that attempts to measure a player's overall efficiency already chooses a weight to assign to offensive and defensive rebounds. Those valuations differ between the different stats, but they all have their reasons (well, except PER, which seems to be pulled straight out of Hollinger's ass).
Bold 1 - I agree, but we could still do this. It would just need to be adjusted.

For example if we use the current equation for a possession using last years numbers.

*All per game league averages

pts per game = 96.3 FGA = 81.4 FTA = 16.9 TO = 14.6 OREB = 11.4

So what we currently get is 96.3/[81.4 + 16.9(0.47) + 14.6 - 11.4] = 1.04 pts per possession

Using the equation I offered we get 96.3/[81.4 + 16.9(0.47) + 14.6 = 0.93 pts per possession

So the league currently averages 104 pts per 100 possessions. Using the equation I offered we get 93 pts per 100 possessions. You can ofcourse do the above and calculate each individual teams average possessions, rebounds per possession, assists per possession etc etc etc. Then compare against the league or another team etc.

Its the same method, with a different equation and therefore different results. So one can still get per possessional efficiency, its just going to be different than what it currently is. (each action per possession will on average be less valuable than how its currently calculated)

I'd argue that accuracy is more revealing than convience. Personally I think measuring the equation by using -OREB is definetely more convient. 1) its always been that way, so continually measuring it that way is convient (especially when comparing against historic numbers). 2) it makes possession equal (in any given game) which makes it easier to compare at a game level.

BUT, if its less accurate than thats not really an excuse. Or atleast shouldn't be. It would be an absolute ton of work to go back and 'correct' old data - yet if we can make that work more accurate, its benificial in the long run

Bold 2 - I'm not saying its necessarily better (I mean I DO think it is, but thinking it is and it being so are two different things). What I really want to know is why does a possession need to be considered over only when the ball changes hands as opposed to when the shooting team gives up control? Or why is that a more reasonable way to value it? It seems rather arbitrary when we consider the rules of the NBA. Its not illogical, after all in most sports we consider a possession over when the ball changes hands. But NBA basketball, with its unique limit on how long one can control the ball (ie. the shot clock) may demand a different view.

Both equations I provided are simple measure of the number of possessions. The say nothing other than 'how do we measure a possession'. But this is also what all box score stats are derived from - its from here they get the estimated value of any actions. So if the average number of possessions per game changes, it will definetely effect the value of all statistics in a game. (as I showed by pts/possession)


Bold 3 - I kind of addressed this already, but it most definetely will effect how each individual players action is valued. Without going into too much detail, how rebounds and missed shots are measured are signficantly different, resulting in much different values (it is one of, if not the, greatest inconsistency between metrics). This would completely alter how PER or WP goes about measuring those particular statistics. I can go into alot more detail into that, but it would have to be extensive and so I don't want to do that without you (or anyone) interested in a more extensive explanation.