Okay, a coach doesn't necessarily like to hear the rationale, "That wasn't in my area, coach." After all, he probably doesn't know anything about PCA's. And he's just ragging on you as the nearest representative of the crew on the floor, either expressing frustration over something called or missed, or lobbying for future favoritism -- neither of which have a high likelihood of meriting our serious consideration (yes, there are exceptions to that). Therefore, what often works is to just somehow fill in the time until his attention is diverted to the next play occurring. My latest favorite goes something like this:
Coach: How could your partner call that over there. Didn't you see that?
Me: Coach, I understand you disagree with that call over there, is that correct?
Coach: That's correct.
Me: I understand.
Coach:
Me:
... and on to the next play myself.
By that time the coach's attention is diverted to the next play, and if he wants to continue the point, which he probably won't (when I was in his place my memory was about as short as my tallest player--not very) and if he wants to rag on my partner for his part in his perceived debacle he'll at least wait for him to come around or, more likely, just drop it.
Kinda a perverted "Verbal Judo" tactic, but it works.