I just find it weird that the only two people he keeps a picture of in his room are himself and Link. If he was as obsessed with Zelda as he pretends to be, he would have at least a small drawing of her on his table or something. But no. Link is there tho.

I think he put it on a punching ball only to be taken seriously by his sidekicks. I mean imagine you're a bully and when your friends come in your room, they find out you've been drawing your "enemy" and pinning it on the wall. It would've just been too embarrassing.

Still, confident cliche jocks rarely crumble in front of their crush. Look at Gaston from beauty and the beast. When he sees Belle, sure, his behavior changes, but he's still a showoff. Groose just seems mildly uncomfortable.