[crew]

wow, i like how everyone is discussing this. i personally would call a common foul, it sucks but this could lead to retaliation later in the game.
as the glancing punch was landed i would blow my whistle and just hold up my fist with no type of signal(common foul in mind).i would then watch the reaction of the punched player.
if he came up after the player that punched him i would call the punch a technical(i would not eject for fighting).
if the punched player came up swinging i would eject both for fighting.
i feel that if you blow your whistle on this play(do not be quick to signal) but watch the reaction and the out come of what happens before assessing penalties.

in the instance of this thread starter i would call a common foul on the player that inadvertantly punched the opponent. though i do see the point of view of the guys who would not penalize, i think you have to be there and have a feel for the type of game and your call should fit the game.