It sucks that a few nasty apples (exploiters) make us devs have to do extra work to keep the game fair! UGH!
But yes, as @colbert2677 stated, you need to track
if finalPos - startPos > someSpeedLimit then
--Go to town here.. log their name, crash them in a horrible way,
--as long as you're sure this script won't trigger on innocents
--(I'll get to that) go do horrible things
end
As I mentioned, if you have vehicles or abilities that make you increase speed in your game, you need to be aware of these. If someone is in a boat (that is faster than walking) they can be picked up as an exploiter when really they are just using a vehicle. Make sure to maybe include in the speed limit maybe the absolute max speed a player can go.
SO much work… I hope you find a solution!!