How to track a player's KO's in a game?

Here, maybe this could help get you started:

local Players = game.Players

local Template = Instance.new 'BoolValue'
Template.Name = 'leaderstats'

Instance.new('IntValue', Template).Name = "Kills"
Instance.new('IntValue', Template).Name = "Deaths"


Players.PlayerAdded:connect(function(Player)
	wait(1)
	local Stats = Template:Clone()
	Stats.Parent = Player
	local Deaths = Stats.Deaths
	Player.CharacterAdded:connect(function(Character)
		Deaths.Value = Deaths.Value + 1
		local Humanoid = Character:FindFirstChild "Humanoid"
		if Humanoid then
			Humanoid.Died:connect(function()
				for i, Child in pairs(Humanoid:GetChildren()) do
					if Child:IsA('ObjectValue') and Child.Value and Child.Value:IsA('Player') then
						local Killer = Child.Value
						if Killer:FindFirstChild 'leaderstats' and Killer.leaderstats:FindFirstChild "Kills" then
							local Kills = Killer.leaderstats.Kills
							Kills.Value = Kills.Value + 1
						end
						return
					end
				end
			end)
		end
	end)
end)

So pretty much in this script, its a leaderboard for the players kills and deaths. Now, if you were wanting to just have the KO's and not have the deaths, it would look something like this:

local Players = game.Players

local Template = Instance.new 'BoolValue'
Template.Name = 'leaderstats'

Instance.new('IntValue', Template).Name = "KO's" --- Name of what you want your scoreboard to say EX: Kills, KO's

Players.PlayerAdded:connect(function(Player)
	wait(1)
	local Stats = Template:Clone()
	Stats.Parent = Player
	Player.CharacterAdded:connect(function(Character)
		local Humanoid = Character:FindFirstChild "Humanoid" ---- Naming the humanoid in the game.
		if Humanoid then
			Humanoid.Died:connect(function() --- On the players death, these lines of code run.
				for i, Child in pairs(Humanoid:GetChildren()) do
					if Child:IsA('ObjectValue') and Child.Value and Child.Value:IsA('Player') then
						local Killer = Child.Value
						if Killer:FindFirstChild 'leaderstats' and Killer.leaderstats:FindFirstChild "Kills" then
							local Kills = Killer.leaderstats.Kills
							Kills.Value = Kills.Value + 1 ---- Adds 1 to the Kill value or in your case, the KO value.
						end
						return
					end
				end
			end)
		end
	end)
end)

In this script, I removed the new instance stated deaths, and all of the death coding in the script. I also changed the name of Kills to KO's for you. Hopefully this helps you at all.