I'm with TxMike, as long as the contact is just a block, which can be a push. Contact that is violent or otherwise intended to solely punish an opponent, or is on a defenslesss player is not part of football, and is to be penalized. But, in the case described, it seems like just a part of football, even if it wasn't really necessary. You can easliy argue that the defensive player was legally blocking a potential tackler of the kick returner. And he certainly isn't "out of the play" or defenseless. Let 'em play.