If you've been to a baseball blog before, you've probably encountered the phrase 'small sample size.' It's a useful reminder that numbers need time to stabilize and that several factors can obfuscate a player's statistical record over a short time frame. To put it simply, statistics used hastily can sometimes paint an inaccurate picture of a player's skills and abilities. And I sort of wonder if that has happened to John Jaso.
Jaso, as you probably know, has been the Mariners best hitter this year by a fairly clear margin. He leads the team in average, OBP*, slugging, ISO, and by extension, wRC+. He has done so while catching a fair number of games, walking more than he's struck out, and hilariously, chipping in four steals without being caught. It's an impressive batting line that comes with just one caveat: he's only had 47 plate appearances against lefties.
*- Horrible, no-fun no-good fact uncovered in this exercise: Mike Carp has the team's second highest on-base percentage. Mike Carp has a .319 OBP.
Jaso has a reputation as a weak hitter against lefties. Much of this stems from his admittedly poor aggregate performance against major league LHP's, particularly in comparison to his strong numbers when he has the platoon advantage. See the difference:
At first glance, that looks pretty stark. However, as you might have guessed at this point, that line against lefties comes in a very small sample, as just 145 of Jaso's 1,016 career plate appearances have come against southpaws. That's hardly a large enough body of work to permanently relegate an otherwise fine player to a life of platoon duty. In fact, a couple of other metrics suggest that Jaso might be just fine without the platoon advantage: Jaso has a higher career walk rate against lefties (BB% is a metric that stabilizes quickly) and his other numbers are dragged down by an unsustainable .208 BABIP.
The BB% demonstrates that Jaso is seeing the ball well against lefties, while the BABIP insinuates that Jaso is due for a bit more fortune in the batting average column than he's had thus far. And while Jaso's minor league numbers indicate that he's always been better against righties, the totals are hardly divergent enough to declare that he's never had success against lefties.
To be sure, Jaso's batting rates this season would almost certainly be lower if he'd faced a significant number of southpaws. He doesn't hit for much power against lefties (a trend that dates back to his days in the minors) and his strike out rate is nearly twice as high as it is against righties (though still lower than many of the Mariners regulars.)
But Jaso has been the Mariners best hitter this season and he has earned the opportunity to face more lefties. While his performance against lefties doesn't match up with his success against righties thus far, he's essentially competing with Miguel Olivo (and his not-so-stellar 71 wRC+ against LHP's over the past two years) for playing time. Jaso has a pretty substantial advantage with the bat over Olivo already, and there's at least a chance his numbers against lefties would improve with more consistent playing time.
Ultimately, John Jaso has been a revelation for this club and he will almost certainly enter 2013 as the starting catcher. In the name of evaluating one of the cogs to next year's team, Eric Wedge ought to give Jaso plenty of at-bats against lefties down the stretch and early next season. If he struggles, the M's can continue to platoon him with a right handed hitting catcher going forward. But if Jaso's numbers pick up a bit, the M's will have found an even more valuable piece than they have already. I just don't see a downside to letting him face lefties consistently over the rest of 2012.