This would work too. But, if an exploiter suddenly wants to attack players instead of NPCs, this would not work. Also, this doesn’t stop click to teleport scripts either (maybe an exploiter chickening out in a fight). This idea would be MUCH simpler (although you still have to calculate acceptable speeds) but only practical for attacking the NPCs.
If he only wanted to guard the NPCs, then it would be even simpler and more reliable to use @AwesomePossum212’s amazing trap idea.
Although, you did just indirectly point out a flaw in my system: if a player somehow gets flung at high speeds, they would get picked up as teleporting.