How deep was the bench?

In the comments, the subject has come up of the depth of the bench in the IBL - or, rather, the lack of depth. With just 20 players per team and the rosters fixed at the start of the season, teams had no way to make up for players whose performance fell short. They couldn't just bring someone up from "the minors" midseason, since there were no minors to draw from.

Add to that the great variation in skill levels among players, whose backgrounds ranged from high levels of play such as Japan and AAA, all the way down to rookie ball, college ball, college ball a decade ago, and the Israeli amateur leagues. As Coach Scott Perlman of Bet Shemesh put it, "I feel our starting team for the Blue Sox could play a AA team and be competetive, but over the course of a series, we would not be able to match that level, because our bench was nowhere near strong enough, and doesn't compare."

Can we measure depth of bench? I don't know if there's an accepted way to define the bench, but I picked a common sense, though far from perfect, approach: Take the nine players with the most plate appearances for each team, and call them the starters. Everyone else is the bench.

For the IBL, that yielded 54 starters for the nine teams. They had 85% of the plate appearances over the season. Everyone else was the bench. Their summary stats:

                 AVG   OBP   SLG 
IBL             .270  .383  .411
Starters        .289  .401  .445
Bench           .170  .274  .223
Bench/Starters  58.9% 68.4% 50.1%

Not surprising, the same calculation yields very different results for the majo leagues. Again, the "starters" are the nine players from each team with the most plate appearances, totalling 75% of the season's plate appearances.

                 AVG   OBP   SLG 
MLB 2007        .268  .332  .422
Starters        .279  .345  .446
Bench           .237  .292  .353
Bench/Starters  84.9% 84.5% 79.1%

With poorly performing or injured players easily replaced from the pool of minor leaguers, major league teams have a much greater margin of error than our under-resourced IBL teams.

Notice that the stat lines for IBL starters were a bit higher than their major league equivalents (actually, substantially higher if you include reaching base on error, but that's besides the point). But the bench players had much lower stats than the bench in the MLB.

I haven't tried the equivalent for pitchers (yet), but I assume the results would be similar.