Anti-Team Kill [When a player TKs then they get killed and deduction of Credits] Any Help?

stats in line 44 is always nil, and therefore the credits are never reducted. Supposing that by stats you meant leaderstats, you should instead do what i did there:

print("TK script loaded.")

function onHumanoidDied(humanoid, player)
        local killer = getKillerOfHumanoidIfStillInGame(humanoid)
        if (killer ~= nil) then
        handleTKs(player, killer)
        end
end

function onPlayerRespawn(property, player)
    -- need to connect to new humanoid

    if property == "Character" and player.Character ~= nil then
        local humanoid = player.Character.Humanoid
            local p = player
            local h = humanoid
            humanoid.Died:connect(function() onHumanoidDied(h, p) end )
    end
end

function getKillerOfHumanoidIfStillInGame(humanoid)
    -- returns the player object that killed this humanoid
    -- returns nil if the killer is no longer in the game

    -- check for kill tag on humanoid - may be more than one - todo: deal with this
    local tag = humanoid:FindFirstChild("creator") --findFirstChild is deprecated

    -- find player with name on tag
    if tag ~= nil then
        local killer = tag.Value
        if killer.Parent ~= nil then -- killer still in game
            return killer
        end
    end

    return nil
end



function handleTKs(player, killer)
    if (killer.TeamColor == player.TeamColor) then
    killer.Character.Humanoid.Health = 0
    killer.leaderstats.Credits.Value  = killer.leaderstats.Credits.Value - 500 --leaderstats are included per player, you must refer to it inside killer.
end

function onPlayerEntered(newPlayer)
        while true do
            if newPlayer.Character ~= nil then break end
            wait(3)
        end

        local humanoid = newPlayer.Character.Humanoid

        humanoid.Died:connect(function() onHumanoidDied(humanoid, newPlayer) end )
        newPlayer.Changed:connect(function(property) onPlayerRespawn(property, newPlayer) end )
end

game.Players.ChildAdded:connect(onPlayerEntered)

I also replaced a deprecated function. This should work now!