I'd meet with that pitcher privately. I would then ask "Suppose you're pitching your backside off, inning after inning, only to find your shortstop couldn't field a ball to save his life. Making matters worse, when he's up to the plate, he swings like a gate!"
So you approach him in the dugout and ask.." what's with you? I'm out there busting my hump and you're sucking wind?"
He looks you square in the eyes and tells you.. " I have trouble concentrating."
Ok, now you take it from there.
Meanwhile, you see your pitching coach making two phone calls - one to the bullpen, and the other on his cell phone. Now you know what the bullpen call is for, but, can you guess who he's talking to on his cell phone?
In competitive baseball, lack of concentration is an excuse, not a reason. If a pitcher can't concentrate then he doesn't belong on the roster - period. Sooner rather than later, a man's teammates will give the cold shoulder along with some not so nice payback. On the other hand, with park-n-rec, fun ball and the like, I wouldn't be too concerned.