Subs are non-starters who 'sub in' off the bench.
Using pages like this one: http://bkref.com/tiny/M8Kn2
In a single season, from 1999-00 to 2010-11, in the regular season, player did not start game, sorted by descending Minutes Played.
I sorted by Games, then copied every player season of fewer than 64 games (as a substitute), from almost 2000 minutes down to 640.
This selection allows for significant games as a starter; and I found 470 players in this century who also had at least 480 minutes as a starter in the season; all at least 14 games.
The theory: A given player is essentially the same player at all points during a given season; and then we can see whether he's better suited to starting or to coming off the bench. Individual teams likely have kept track of these things all along.
But what is typical? Is it relatively easier to score, rebound, etc, when you are off the bench, presumably playing with and against fewer starters? Or are some things easier when your teammates are mostly better than you are?
This study doesn't include any full-time starters, nor any scrubs. These are players who started at least 14 games (and >480 min) and also came off the bench in at least 23 (>640 minutes).
Here are the averages -- totals divided by 470 -- per 36 minutes:
per36 MPG FG FGA FG% 3fg 3fga 3fg% FT FTA FT%total
sta 31.2 5.10 11.35 .449 .95 2.59 .365 2.38 3.11 .764
sub 21.5 5.01 11.41 .439 .99 2.81 .353 2.57 3.41 .754
per36 ORb DRb Reb Ast Stl Blk TO PF Pts total
sta 1.63 4.24 5.87 3.10 1.10 .58 1.94 3.04 13.51 22.23
sub 1.67 4.24 5.92 2.82 1.14 .63 1.97 3.54 13.59 22.12
is just Pts+Reb+Ast+Stl+Blk-TO
As subs, these players shoot more often but with less accuracy, vs starting; perhaps fueling the increase in OReb (yet not DReb).
Harder to get an Assist and easier to get a foul, when you're not starting.
Note: A similar study of just the current season had some similar results. The difference in OReb% was more exaggerated, as I recall.