But it seems to me that the saber guys aren’t trying to measure what happened. As a practical matter, they are attempting to predict what will happen next. So, for example, they are interested in how likely it is the guy will get on base in the next at-bat. Therefore they want to look at his OBP, which measures how often he got on base before, but deep down they’re not interested in it as a record of what happened, but only insofar as it is an indicator of what will happen.

But I often sense that it’s more than just prediction. The stats-geeks I encounter in discussion seem to be driven by a desire to measure how good each player is. But they aren’t satisfied by measuring what he has actually achieved (which might be due to “luck”); rather, they want to know how good he “really is”. This is where it starts to feel “Bayesian” to me, as I understand the idea. They are postulating that there is some underlying measure of how good a player that guy is, and all the new formulas they invent are efforts to capture that underlying truth.