Where would I put this anti-walkspeed script in the game to make it work?

Where should I place this?

local MaxSpeed = 16 -- Max speed possible in game

-- Note: I've added a rule-counter, which means you have to go too fast for 2 ticks to get punished.
-- That's necessary for teleporting by spawning, maybe your admins tp'ing, entering a vehicle, ...

local caught = {}
local function punish(plr)
    if caught[plr] then
        -- More than 2x too fast in a second? Seems like he needs to get punished
        -- (As far as I know, it's impossible to teleport 2x in a second without exploiting)
        -- (Assuming that people don't use admincommands teleport/ very fast)
        -- (Also assuming that the game doesn't teleport someone 2x in a second)
        if tick() - caught[plr] < 1 then
            -- Should never fail, as we don't check RobloxLocked players
            -- Even if it fails, punish() is called in a pcall() so it's safe anyway
            plr:Kick()
            print(plr,"kicked for speed hacking") -- Print in Server Console
        end
    end caught[plr] = tick()
end

-- We don't want to flood the caught table with offline exploiters who were here, don't we?
game:GetService("Players").PlayerRemoving:connect(function(p)
    caught[p] = nil -- remove old unneeded data
end)

local function ignoreState(state)
    if state == Enum.HumanoidStateType.Running then
        return false
    elseif state == Enum.HumanoidStateType.RunningNoPhysics then
        return false
    elseif state == Enum.HumanoidStateType.StrafingNoPhysics then
        return false
    elseif state == Enum.HumanoidStateType.Climbing then
        return false
    elseif state == Enum.HumanoidStateType.RunningNoPhysics then
        return false
    end return true
end

while true do
    --[[ Saving the current position (position just before the tick change) ]]--
    local pos = {}
    for k,v in pairs(game:GetService("Players"):GetPlayers()) do
        if v.Character and v.Character:findFirstChild("Torso") then
            -- Renamed/Absent Humanoid? Oh well, can't predict that
            if not v.Character:findFirstChild("Humanoid") then return end
            local human = v.Character.Humanoid -- need to use it a lot
            -- Torso can be flinged away on dead, making false results
            if human.Health == 0 then return end
            -- If he sits, we assume he's in a vehicle, thuss may go faster
            if human.Sit then return end
            -- If he's platformstanding, we assume he's skating or so
            if human.PlatformStand then return end
            -- only check if the player is actually running
            if ignoreState(human:GetState()) then return end
            -- Save current position, for comparing during the next loop
            pos[v] = v.Character.Torso.Position
        end
    end

    --[[ Max Distance Calculation ]]--
    local tim = wait() -- Get how long the last tick happened
    local dis = (MaxSpeed + 2) * tim -- Get the max distance someone can move in that time interval
    -- (MaxSpeed + 2): 2 being a safe margin. (Weird calculation? Jumping while running?)

    for k,v in pairs(pos) do -- Time to see if he went too fast
        pcall(function()
            if v.Character and v.Character:findFirstChild("Torso") then
                if not v.Character:findFirstChild("Humanoid") then return end
                local human = v.Character.Humanoid
                if human.Health == 0 then return end
                if human.PlatformStand then return end
                if human.Sit then return end
                if ignoreState(human:GetState()) then return end
                -- Yeuy! Get the distance calculated!
                local d = (pos[v] - v.Character.Torso.Position).magnitude
                if d > dis then pcall(punish,v) end
            end
        end)
    end

    wait(0.1) -- Just to make this a bit more performance-friendly
    -- (Not that it's very unfriendly, though, unless there are 100 players)
end