"Who let him on the stage?" my friend muttered as we scuttled out of The King's Head theatre in Islington recently. Sadly, I didn't have to ask which actor she meant. We'd just seen Kvetch, and at the interval were raving about how superlatively funny it was. So far, so easy to review. Unfortunately, there was one actor (in the cast of five) who almost ruined the second half. I had no desire to ruin his day, or to be cruel for the sake of a pithy one-liner, but my honest response to the play was that while the other four were superb, he let the play down.

Then again, to me, and to my companion at the show, this poor guy was quite obviously miscast – not only was he not right for the role itself, but he grated when put in the incredibly stylised production where the other actors shone. But whose fault is this – is it the acting or the direction? Without sitting in on a play from casting through rehearsals to performance it's hard to know for sure, but I lean towards laying blame at the director's door; surely he or she can see that one of the cast is struggling? Should they not then either re-cast or work to coax a subtler performance from this actor? If the director cannot do this, then either the actor should never have been cast, or the director is not equipped to draw a good performance from the whole ensemble.

Yet blaming the director surely absolves the actor of responsibility for their own performance. It is hard to believe that a performer can be so utterly un-self-aware that they cannot tell when they are the odd one out, or, at the most basic level, fail to notice that they are speaking louder than everyone else. In such a small ensemble, if it doesn't gel well together, the other cast members must notice, too. Perhaps, then, this was not a miscasting problem, but a clear directorial decision? Perhaps he was supposed to act like that? Well, maybe. Without asking the director, I'll never know, but if it was a deliberate choice then it becomes easier, to my mind, to blame the director.

Perhaps it makes more sense to strike a balance, whether as an audience member in the pub afterwards or as a critic, between blaming the actor and the director. But then, directors are quick to claim a share of the credit when a show is roaring success, so, I would argue, they then have to be prepared to accept the flak when one element of a show is glaringly unsuccessful. In the end, then, maybe it's the director's fault. Or maybe it was me.