For the longest time now, we've had it drilled into our heads that Matt Joyce is a platoon player. Or, to be more accurate, that he has a large platoon split and should not be used against left-handed pitchers. Joe Maddon loves to optimize his lineup and place hitters in a position to succeed, so for the past few years, Joyce has never seen more than 100 plate appearances against left-handed pitchers.
This year, though? Due to part to the rash of injuries -- and, I think, in part to Maddon wanting to play Joyce against more lefties -- Joyce has seen his playing time against lefties explode. He already has 40 plate appearances against left-handed pitchers, putting him on pace for around 160 PAs on the season -- or in other words, close to a full-season load for a regular starter.
Since we're dealing with a split, it's still way too early to begin to draw any definitive conclusions about whether the experiment has been a success or flop. But we can begin to get some idea of if Joyce is thriving in that sort of a role, or if he truly is out of his depth against lefties. It's not exactly like Maddon has a choice right now, but once players start returning from injuries, the question is going to loom large: should Joyce continue to start against both hands, or should Maddon turn him back into a platoon player?
I'd be remiss if I didn't start off by mentioning that Matt Joyce has been the Rays' most productive offensive player to date this season. Evan Longoria was off to a blazing start to the year, but if you want to look at overall total production, Joyce has surpassed him by virtue of his crazy hot start (.410 wOBA currently) and his playing time (41 games, 153 PAs). It's difficult to imagine the Rays taking him out of the lineup right now, especially considering how Carlos Pena and Luke Scott have had up and down results so far.
But despite his success, Joyce still has a very large platoon split. He's hitting .305/.416/.632 against RHPs so far (.443 wOBA), while he has a mere eight hits against LHPs (7 singles, one homer). That's good enough for a .657 OPS and .303 wOBA, but it's not exactly something to write home about. And to top it all off, his underlying skills against lefties haven't seemed to change; he's still striking out over 30% of the time against them and his power is actually down so far, so his success has been based on a .368 BABIP. That's not exactly an encouraging sign.
All these signs seem to point at Joyce still being a platoon player...but I'm not so sure. At full strength, it's probably most optimal for the Rays to bench someone that struggles against lefties in favor of Jeff Keppinger, but I don't think that means Joyce couldn't play full time. Consider...
Over the past two years, Joyce has performed better against lefties than Carlos Pena -- around 15% below average offensively versus around 30% below average. His wOBA against lefties has hovered around the .300 mark (.292 last season, .303 this season), and his split against lefties isn't all that bad in the large picture. There are many full-time outfielders that post a split against lefties below that level*, and a .300 wOBA against lefties would place Joyce smack in the middle of the outfield leaderboard. If you consider that Joyce also mashes right-handed hitters and plays above-average defense in right field, I can certainly see the case for him being considered a full-time player.
Through his career thus far, Joyce has been stamped with the label of a platoon player. If he was on most other teams besides the Rays, though, he would almost surely be playing full-time by now and attracting more widespread attention. He's not exactly a superstar player, but he's on pace for another year right around the +4 win level -- putting him right on the cusp of "above average" to "borderline all-star candidate".
One of these days, Joyce will shed the label of being a platoon player, and he doesn't even have to play much better against lefties to warrant it. He simply needs to get the playing time.