A roundhouse kick whether it be high or low isnt hard to defend against. Just step towards the attacker. When they are begining to kick, step in and then their foot wont hit you like a speeding hammer, but their thigh will make contact, causing a reduction in over all speed. Once you step in its fair game, do what ever cuase if your practice it enough, you can really mess them up. Most people doing this kick wont be able to keep their balance if you come in on them while executing this kick.