Black plays for black. The black knight blocks the only position that the black king can move to for safety, all other moves by the black king (or not moving the king at all) result in the king being captured. If it moves right it gets captured by the rook, move down or down-right, it gets captured by the white king. Don't move and it gets captured by the rook, and there's no way to play the black knight to block the rook, either.

Of course you could argue that if you're ignoring today's rules of the game that you may as well have the black king take the black knight, but that's illegal under the rules and probably has been right from the start.