Unsure performance is often an issue with high school and college player, those who are unsure of what they are doing, and who retract back "into their shell" as a result. Timidity is nothing new, and everyone has experienced it at one point or another.
We saw a performance of Threepenny Opera at Northwest Florida State University (or whatever they call it these days) where the pit had been filled with the proper instrumentation, but where the keyboards, trombone and drums were the only "sure" players. Extreme balance problems, and the conductor was so busy minding his new (and showy) keyboard "dude" that he paid little or no attention to anything else. But, what are you going to do?
(They also had a leggy blonde babe filling the part of the Streetsinger. Very attractive, had all the right movements for being on stage, but who couldn't sing a lick. I imagine that she was someone's secret student girlfriend - there were no other reasons for her being there other than for her looks.)
A couple of years ago, we saw a production of Chicago where the Reed 3 babe (also an attractive woman, right up there on stage) completely blew both of the baritone solos and much of the bass clarinet work. This one particularly pissed me off, as I had aced the parts as a young twenty-something when the original Broadway touring company had come through Saint Louis, and I pretty much sight read the whole book.
(But, the worst thing is that she is apparently a pet of the conductor (also a woman), as we have seen her in a couple of other productions (where she did better). It's all I can do not to volunteer that I would bring my horns along and play in their pit for free (the Pensacola Little Theater Company probably could use the financial help).
When I play alongside student performers, I try to urge them to play out (the biggest problem) and to hit as many of the notes as they can. Playing through performance anxiety is something that will come in time; practice makes perfect (or nearly so).