That's certainly how a Night Fury fights, as is evident from the way the dragon arches his back. He's slashed, severely limiting his movements. Overall, he'd be doing a lot better if he could move around properly. Toothless' fighting style blooms under freedom of movement. Here, on the chess board, it's somewhat impossible. He snarls again, standing lower to the ground on account of those injured joints, and bites at the closest of Yousuke's legs.