Pretty much the only thing I have for this is if a person can teleport to where they can see if they go and punch someone if they teleport behind at the last second couldn't they punch them they have pretty much no defence unless they can block both areas at the same time
Also in order to teleport they'll appear just there but air is already occupying the area so if they teleport they would have to clear a space of every atom the before they could teleport otherwise they would end up with air in their blood stream and other stuff and since. If when they teleport would they switch places with the air or push it out of the way. If you teleport and dont switch places the vaccum would suck in air as much as it can so if they touch the person and teleport but it doesnt take the person then they will be sucked towards the vaccum with the rest of air. Also if it teleports a small amount of the air surrounding the person and they're touching someone and you cant teleport multiple people. Through touch then that would theoretically take away a chunk of the person depending on how much of the surrounding area is teleported.