If you're not too busy not being at Soxfest and showing off one of your Jerry Owens jerseys, why not discuss the merits of a full time catcher platoon in 2011?

A few days ago while discussing questions for fans to ask at Soxfest, I wound up going off on a bit of a tangent as to why I think Ramon Castro and A.J. Pierzynski should be platooned at catcher this season. (Just to be clear, when I say platooned, I mean that when the opposing team's starting pitcher is left handed, Ozzie would start the right handed Castro, and against right handed starters, Ozzie would start the left handed Pierzynski at catcher.)

A platoon isn't much good, of course, unless the two players involved actually give you a platoon advantage. For this to work, Castro has to hit lefties better than AJ, and vice versa. Last year was an up year for Castro and a down year for Pierzynski, and in his limited PAs (128) Castro put up much better rate stats than AJ all around. His overall .278/.328/.504 line was good for a wOBA of .362, much better than AJ's .270/.300/.388 line (which game him a wOBA of only .299- ouch).

The result of that relative upness and downess was that Castro's splits were better than AJ's all around: Castro crushed lefties to the tune of a .286/.324/.629 line and a.406 wOBA, clearly superior to AJ's .250/.294/.384 and .288 wOBA. However, his strong offensive season also resulted in Castro putting up a line of .275/.330/.450 with a .341 wOBA against right handed pitching, besting the struggling Pierzynski's .276/.302/.401 and .306 wOBA.

But Baron Underbheit was up, and AJ was down, and both are likely to regress toward their career means. For Castro, this means getting closer to his career .237/.310/.423 (.314 wOBA) and for AJ the good news is he should get closer to his career line of .284/.324/.424 (.321 wOBA). Their platoon splits should also regress to their career lines, meaning we should see Castro hitting closer to .262/.336/.488 (.353 wOBA) against lefties and .233/.302/.429 (.313 wOBA) against righties, while AJ should move toward his .263/.290/.390 (.297 wOBA) line against lefties and .291/.334/.433 (.330 wOBA) against righties.

But AJ is 34 and Castro is 35, and they're both likely to be headed downhill offensively. Unless AJ turns out to be Carlton Fisk, his wOBA against lefties isn't likely to move above the .300 mark. But "likely downhill" isn't exactly useful for forecasting offense. Luckily, some guy named Bill James made up some numbers, and they're posted on some website called Fangraphs which maybe probably exists and happened to be open in my browser, which is good enough for me to use 'em.

This Bill James fella projects Castro to regress quite a bit, to a .239/.304/.439 line and a .325 wOBA. However, that is still a pretty decent improvement over his career line. James isn't so big on AJ, whom he projects will hit .276/.315/.403, good for only a .304 wOBA, quite a bit down over his career numbers. His numbers also project a surprisingly high number of games for Castro which he's probably unlikely to reach, but they're there so we're gonna stick with them.

Unfortunately, these projections don't include splits, at least that I saw. I couldn't find any projections at all that did include splits, so the obvious solution is to perform all sorts of sketchy math on the numbers until they resemble splits projections.

My methodology is as follows: take split number (such as wOBA). Divide by career number. Multiply by projection number. Simple, stupid, probably not even close to being accurate. Let's look at the results anyway, because if you've read this far you probably have nothing better to do:

This advanced baseball number crunching suggests that Castro will hit something along the lines of .264/.329/.506 against lefties, with a .365 wOBA, and .235/.296/.445 against righties for a .324 wOBA. Not bad at all- I'd take that out of a backup catcher.

The totally scientific baseball analytics aren't so kind to AJ, though, projecting him to hit a dismal .255/.282/.371 with a .281 wOBA against lefties, and only .283/.325/.412 with a.313 wOBA against righties.

That doesn't seem quite right- and it almost certainly isn't. I'd put the odds of Castro hitting righties better than AJ in 2011 at a totally scientific slim-to-none. It's hard to see Castro besting his career numbers for two years in a row, and it's also pretty hard to see AJ struggling as much as he did last season again. That sure was a lot of words to draw the following conclusion: if Castro comes close to his projected .365 wOBA against lefties and AJ comes close to his projected .281 wOBA against lefties, the White Sox would have to be crazy to start AJ against a left handed pitcher.

(Note: the White Sox totally are crazy. Mark Kotsay had a .052 wOBA against lefties last season, and that was with a .000 BA. He walked twice, and that was the sum total of his offense against lefties all season. And yet, last season Mark Kotsay started a game at DH against a left handed starter.)

Ah-ha, but you'll say, what about the difference in production that comes with adjusted playing time?  The very same question was posed by blackoutsox, and it's a very good one, worthy of copying and pasting a whole bunch of text which tries to determine the difference in playing time that a platoon would produce.

Last season, the Sox faced 40 left handed starting pitchers and 122 right handed starting pitchers. That’s strangely close to the amount of starts split between Pierzynski (123 starts) and the Sox backups (39 starts). Castro did miss some time, allowing Donny Lucy to take five starts from him, but if memory serves that was caused by a family emergency rather than an injury. Still, he managed 31 starts, and I think that 40 wouldn’t have been too much of a stretch for him. In fact, he started a good number of games with the Mets, 46 as recently as 2009 and 57 in 2005. While he is getting up there in years for a catcher (35 to start the season) he has less than 2800 innings on his knees, and I haven’t seen anything that would be a red flag regarding his durability.

It seems like last season, at least, platooning AJ and the right handed backup corps would have resulted in only one game’s difference in starting time. Hard to say how that might have impacted entering the game as a pinch hitter or defensive replacement, but I’d call that impact minimal.

...

Since 2000, the Sox have faced up to four times as many right handed starters as lefties, and as few as and and a half times as many righties as lefties. This I’m sure is based on several different kinds of science, as well as probably who other teams in the division have on their rosters. The main takeaway to me is that while the Sox did face their fewest lefties since 2002 last season, they weren’t that far off from the average in this totally arbitrarily picked time span. The actual average is 46 left handed starters per season, but given that I didn’t toss out the rather low numbers from the start of the decade let’s just say it’s likely to be around 50.

Even with a total platoon setup, with AJ never starting against a left handed pitcher, that still gives a guy who is currently 34 years old 112 starts per season. While this is a drop in playing time (he hasn’t made that few starts since 2001 when he started 102 games at catcher) it’s not all that significant- only about 11 starts a season on average over his time with the Sox. Given that he’d be sitting for platoon reasons and not necessarily as a day off, he’d also probably be used to pinch hit and end up catching some late innings as well, leaving him on pace to catch another 1000+ innings this season.

Last season, Sox catchers posted a .315 wOBA on the season. My terrible math and projections tell me that this platoon setup is projected to have a .330 wOBA this season- that's an upgrade from Cliff Pennington to Michael Cuddyer offensively, and that only goes up if AJ can climb out of his offensive hole. I think a .340 wOBA is attainable, and that's last season's Johnny Damon territory, a pretty decent upgrade considering it has zero cost and minimal impact on playing time.

The White Sox are sure to be better offensively this season, with all of their Mark Kotsays being replaced with an actual baseball player.  Catcher figures to be one of the weakest offensive positions on this seasons' Sox, and a simple move like a platoon setup which maximizes the potential there seems like a good one.