Occasionally I get asked why such-and-such a player has a True Average that seems out of line with what their OPS (or some other offensive rate) would suggest. There's a lot of potential answers to that — TAv is a bit more precise in how it weights various events, and it has park and league quality adjustments. But I find that most people understand those answers pretty intuitively. There's one that seems to confuse people a bit more often.
True Average includes situational outs in a batter's production. That means that hitting into a lot of double plays reduces one's TAv, and hitting an above-average amount of sacrifices increases your TAv. We recognize that these events are situational — some players have more chances to do these things than others, even if plate appearances are even. So we look at the various base-out states each hitter gets a chance to bat in, and use that to compute our baseline of average to compare to. That way, we don't penalize hitters who came up with runners on and less than two outs for hitting into more double plays than someone who frequently bats with the bases empty.
To illustrate, I went into our database and recomputed TAv for everybody with situational outs runs excluded, and looked at the difference between that an actual TAv. With a minimum of 100 PA, here are the 20 hitters who saw the biggest boost to their TAv from situational outs:
And here are the 20 hitters who have seen their TAv dropped the most by situational outs, again minimum of 100 PA:
It's not necessarily a shocking list — Michael Young leads all of MLB in double plays, for instance (and he hit into another one during tonight's game). But it does illustrate how some things not typically recorded in OPS can have a significant impact on a player's production. Admittedly, for most players, SIT_RAA is going to have little impact, but for a handful it will be important, and in looking at a particular player's offense it could mean the difference between a slightly above-average TAv and a shockingly low one.