Drew Davidson's Wednesday Rangers notes include this nugget:
David Murphy is being used as an everyday player, Ron Washington said. Murphy has been swinging the bat well of late, and is expected to get starts against left-handers the rest of the season. That will cut into Craig Gentry's playing time.
If that's true, it's more than likely a mistake; and an extremely disappointing one.
With a 142 wRC+ against left-handed pitching, Murphy has absolutely been hitting lefties well in 2012, that much is true. That's in a measly 48 plate appearances, though; that's not just a small sample, it's absolutely tiny. The 559 PAs Murphy has against them in his career are far more telling, and that's where he's got a 73 wRC+.
Craig Gentry, meanwhile, has a career 110 wRC+ against LHP, and has even been better against them this year. On top of that, playing Gentry gives the Rangers a superior defensive lineup, keeping Hamilton out of center field, and replacing a solid corner outfielder (Murphy) with a phenomenal centerfielder (Gentry).
The Gentry/Murphy platoon has been a serious bright spot for the Rangers this year, combining for 5.1 Wins Above Replacement (1.3 wins ahead of second place Elvis Andrus if you count them as one person). Ending that platoon makes no readily-apparent sense. Murphy is playing well, but so is Gentry, and there is no reason to expect Murphy to be the better hitter against lefties going forward; and he's certainly not the better defender.
Meanwhile, we also get robbed of how enjoyable Gentry's explosion to becoming a successful Major League player has been to follow.
That said, if Washington can play the hot hand like this, he can certainly change his mind when Murphy regresses to his mean, I assume. There's plenty of time between now and October for that to happen.