By Jason Wojciechowski on May 25, 2012 at 5:50 PM
Over the course of a season, we expect that the pitchers a batter faces and the batters a pitcher faces will more or less even out, assuming regular playing time. (Backups are subject to small-sample issues, and platoon players play selectively in ways that might wreak havoc with any aggregate measure of opponent quality, as we'll discuss a bit more below.) It more or less works out, though not entirely: Emilio Bonifacio, Gaby Sanchez, and Giancarlo Stanton (sense a theme?) faced pitchers last year that aggregated to about 6% better than average in True Average allowed. Ryan Braun, by contrast, faced pitchers that added up to average. Six percent is not nothing, and if we were choosing between Gaby Sanchez and Ryan Braun for MVP, their quality of opponent faced is something we might consider, seeing as how it's almost entirely luck. (In theory, a team that bashes opponents into submission with regularity would more often face mop-up relievers, but I would speculate that any individual player's ability to move the needle in this regard is minimal.)
Matt Kemp, for what it's worth, faced pitchers that were about 4% better than average.
But we're not here to re-litigate the past. Let's look at 2012's list of hitters with at least 50 PA sorted by RPA+ allowed (RPA+ is just the + version of TAv -- number above or below 100 indicates percent above and below league average) by the pitchers those hitters have faced. Hopefully you can click that link without being a subscriber to Baseball Prospectus. I'm not sure, though.
What it shows, in case you can't click it, is that Jonny Gomes is sixth on the list. Since it's ordered from lowest opponent RPA+ to highest, what that means is that Gomes has faced the sixth-toughest pitchers overall, a group that's allowed TAv at a rate 14% below the league average. Note that by using TAv instead of, say, FIP, we're including the entire run-prevention scheme that Gomes faces. This is a fair approach, though, because however we speak about "the batter-pitcher battle," batters don't just fight the hurler. They fight the entire defense, nine dudes all aligned with the single goal of getting the batter out.
That makes Gomes's .304 TAv this season that much more impressive, doesn't it?
It does, although let's talk caveats. First, just like Gomes has only had a quarter-season's worth of plate appearances, the pitchers he's faced have only had a quarter-season's worth of batters faced. Some of them may have had a fluke good game or two that's skewing their overall TAv allowed figures. As the season rolls along, those fluke games will recede in significance and the pitchers' numbers will regress to normal.
This is another way of getting at the fact that the opponent-quality report on BP is not an opponent true-talent report. The numbers are not, as far as I know, regressed toward any average. They're raw reports of what has actually happened on the field (with the standard park and league adjustments that go into TAv). Over a full season, and having faced the large number of pitchers that a batter will face, we hope that these effects will wash out.
There's also an "adjusting the adjustments" question to be asked. What if a weirdly large number of the pitchers that Gomes has faced have themselves faced a weirdly large number of bad hitters? Their TAv-allowed numbers will be depressed below their talent whether they've actually pitched better than their talent or not. (Or whether the defense has defended better than its talent.) Again, we'd hope that over the course of a season, these issues will even out. I can spin myself in circles all day on this otherwise: if the pitchers have faced bad hitters, maybe it's really that those hitters faced good pitchers, but maybe that's just because those pitchers faced bad hitters, but maybe ... well, you get it.
Finally (or not -- if you think of other issues, let me know), Gomes is a well-known platoon player. He's actually got more PAs against righties this year than against lefties, but it's 61-48. Compare Cliff Pennington, who has 121 PA vs. righties and 53 vs. lefties. Gomes thus avoids some righties, and one might speculate that Bob Melvin would keep him on the bench against those righties that are toughest on right-handed hitters. A pitcher's TAv allowed is accumulated against some mix of batters from each side of the plate, while Gomes only ever bats righty. Right-handed pitchers, then, are likely tougher on him than their overall TAv numbers would indicate, while left-handed pitchers are easier on him. Whether this balances out depends on the mix of handedness that Gomes himself faces as compared to the mix of handedness that his opponents face. Being a platoon player likely means that mix is off -- he has the platoon advantage more often than he "should" compared to how often the pitchers he faces give up the advantage. This will, unless my logic is totally wrong, mean that Gomes's pitchers-faced have actually been a little easier on him that the straight number indicates. Does that make sense? I don't know how to quantify the effect, or even if we should bother, but it's another issue worth noting.
I don't want to be misconstrued. None of the above is meant as a criticism of the opponent-quality reports. The idea is to show you a stat, an interesting, useful stat, and to work through the thought process of how to use that stat most effectively, how not to overstate what it's telling us, and so forth. I hope you've found this interesting.