His father hits him once, and only once- knocks him backwards in the kitchen, and his hand lands on the whistling teakettle and the skin hisses and breaks apart.
This sentence doesn't make sense to me. Also, replace your hyphens with dashes (—).
Big, quiet Thomas moves, and he catches the swing against the flat of his hand before it is even really started. The metal leaves a long, sooty mark on his palm, and the next morning the mark has turned to a faint purple bruise.
This also doesn't make sense to me, since I don't know why Thomas is involved in this moment.
Besides that, I generally liked this, but I feel like there wasn't enough attention to plot to merit an upvote.