Although it's not easy, Sickle seems to be allergic to straight punch combos. Immediately start off with a punch combo. When he gets up, try it again. If he dodges your attack, wait until he's finished and then start a punch combo again. Run around the room a lot. Sickle can't be thrown that easily and it's best to avoid that route unless you get lucky. Dodge or block when necessary, but don't rely on it too much as Sickle can grab you when you are blocking.