Any argument that invokes "fans shouldn't have been on the field" is a red herring argument.
Because it doesn't matter. It simply makes no difference.
Why not?
Because the Alabama player didn't smack the fans before they were on the field. He smacked them after they took the field.
They had already committed the grievous sin of getting excited and rushing the field to celebrate (how dare they?).
That having happened, everyone involved must reset their Morality Calculators. Because that part, fans on the field, is now a pre-condition for any decision about "what's the right thing to do?"
And the right thing to do is, obviously, don't hit other people who aren't threatening you. Don't hit a young woman who walks by talking on her cellphone.
It doesn't matter if she's smiling, and you're unhappy. It doesn't matter if she's in your path. It doesn't matter if she's wearing the colors of the team that just beat you. There are no valid reasons--no valid excuses--for hitting another person under those circumstances.
So, for those who want to try the "but she shouldn't have been there" defense, give it up. It's not a part of the calculation at the instant he swings.
Dude acted like a thug. Needs to sit out at least one game, and undergo mandatory anger management training. And if the folks he hit sue him for damages, he can pay that price, too. And if the NFL decides not to give him a chance to hit some other woman while in their employ, that's on him, too.
Bad decision, thuggish behavior.