As usual, we have people who will come in and pretty much absolve the refs of anything they do wrong. Here is the rule in question here:
I find nothing in the rules that specifically states that it is legal to punch the ball, or any statement to that effect. There is not some sort of protected status around punching the ball, the ball is simply fair game if you have a shot at it. There is nothing in this rule that states if there is a question of if the player is punching for the ball, it's not a foul. It's simply common sense that if a player punches a ball from someone's hand, it's legal. From what I could see live, and in every replay after the fact, the ball does not seem to be visible, and it doesn't look like, based on the angle, the Minnesota player had some sort of clean shot at it. So, in effect, he's just wildly swinging his arm and fist, all of which certainly seem against the rule I posted above. It should have been a penalty, but I'm not surprised they didn't call one.
I would be willing to bet everything I own, if the two teams were reversed, flags and hats would have been flying everywhere from every ref on the field. I most certainly wouldn't have a problem with a Nebraska player being flagged for doing that; and I'd be willing to bet the same people arguing it's okay they didn't call a penalty would be the first to argue why it should have been a penalty, and would be the first to say we "got away with one" if none was called.