How do you disable ties, on a KO WO leaderboard, so if you tie, it won't count it on the leaderboard?
First off, are you familiar with the kill tag system? Whenever a tool damages a humanoid, it creates a "tag" ObjectValue in the damaged person's character that refers to the attacker. If a humanoid dies, there is typically a leaderboard script that checks for the kill tag, and increments the Knockouts and Wipeouts.
(More about the kill tag system: http://wiki.roblox.com/index.php?title=Tools#Damage)
So what you'll need to do is modify the onHumanoidDied function in your leaderboard script to only treat it as a kill if: the killer has a character, and the killer's character's humanoid is alive.