The madness of the Cornucopia wasn't entirely unexpected, but Thor is still thrown by the havoc of it all. He hadn't expected tributes to turn on one another so quickly, given the obvious mutual enemy is at fault here. He can see now he's been a little optimistic, particularly when standing back from the tousling has left him empty handed for the moment.

At the very least, he's free to engage in doing what he perceives as the right thing. He certainly won't be shedding the blood of fellow tributes to appease the Capitol, so he might as well make himself useful. He sees a perfectly fine opportunity for that when he catches sight of what is clearly a vicious assault for spoils. He moves fast when he approaches, using the momentum to give Vriska a rough shove to the side so he can put himself between her and Shaggy.

"You are wounded, little one. It would not be wise to engage in battle, and I will not allow you to torment this man any further."