There's this girl that I'm (trying) to game at college. Since I first talked to her, now in the hallways she shakes head while smiling (like saying "no" with her head) or comes up and tries to punch/nudge me. Up until now, I just laughed and told her she should try boxing. I can't think of a really good way to react to that...

I don't see a question in your post, but I will ASSUME that if you were asking a question, it would be "What's a really good way to react to that?"

Any experienced PUA will tell you that you are asking the wrong question because you are focusing on the wrong aspect of the social dynamic between you and that girl. The RIGHT question would be "What's a really good way to be PROACTIVE to achieve my goal of _(fill in the blank)_?"

Worry about how you are going to be PROACTIVE before you worry about how you're going to be REACTIVE.

So, let me pose these 2 questions to you:
1. What are your goals with this girl and with your "love life" in general?
2. What are some things you can do to be proactive in attaining these goals?

Be the cause, not the effect.

Play along. It sounds like she is trying to be playful, take advantage of it. Most girls that are playful have great personalities and are tons of fun.

This is a perfect opportunity to raise her IL with some playful banter.

_________________
Keep people off-balance and in the dark by never revealing the purpose behind your actions. - Robert Greene

I agree. Playful people in general are so much damn fun. But if you keep it at this "playful stage" for too long, this is all you'll ever get.

I'd hit her back just in the face.

the first half of the first sentence of my comment is useful.

Thanks for the advice guys. Your spot on about the really nice personality part! I'll try get that proactive state of mind going, it seems to focus on what I can do to make stuff happen, not wait for it to come to me, right?