I wouldn't be surprised if that counted as catching the giantess flat-footed... I mean, I don't think she would ever see "little guy that only comes up to my kneecaps punching me in the face" coming.

Come to think of it, as long as Roy has the appropriate feats, that might be among the smartest ways to fight her... given that he's already lost his sword twice in this fight, it seems a waste to keep using it.