Basic anti-noclip

--[[note: make sure your game is in r6 since it might give false positives when in r15 especially on small r15 avatars]]

local Players = game:GetService("Players")
local NoclipPart

local function CreatePart(Character, RootPart, Humanoid) -- function to create NoclipPart
    local Connections = {}
    local NoclipPart = Instance.new("Part")
    NoclipPart.Size = Vector3.new(.5,.5,.5) -- set the best possible size without false flags
    NoclipPart.CanCollide = true -- cancollide must be true otherwise it won't work
    NoclipPart.Name = math.random(1, 9999)
    NoclipPart.Parent = Character
    local Weld = Instance.new("Weld") -- a weld so the Part stays attached to the RootPart
    Weld.Part0 = NoclipPart
    Weld.Part1 = RootPart
    Weld.Name = math.random(1, 9999)
    Weld.Parent = NoclipPart

    NoclipPart.Destroying:Connect(function() -- if RejectCharacterDeletions is set to false this'll make sure the part isn't just destroyed
        if Humanoid and Humanoid.Health > 0 then -- checks to make sure the Player hasn't died
            NoclipPart = CreatePart(Character, RootPart) -- if the player hasn't died then recreate the part
        else
            for _,connection in pairs(Connections) do -- loop through all connections and disconnect them
                connection:Disconnect()
                connection = nil
            end
        end
    end)

    Weld.Destroying:Connect(function()
        if Humanoid.Health and Humanoid.Health > 0 then
            if Humanoid and Humanoid.Health > 0 then -- checks to make sure the Player hasn't died
                NoclipPart:Destroy()
                NoclipPart = CreatePart(Character, RootPart) -- if the player hasn't died then recreate the part
            else
                for _,connection in pairs(Connections) do
                    connection:Disconnect()
                    connection = nil
                end
            end
        end
    end)

    return NoclipPart
end

Players.PlayerAdded:Connect(function(Player)
    Player.CharacterAdded:Connect(function(Character)
        local Humanoid = Character:WaitForChild("Humanoid")
        local HumanoidRootPart = Character:WaitForChild("HumanoidRootPart")
        NoclipPart = CreatePart(Character, HumanoidRootPart)

        while true do
            if Humanoid and Humanoid.Health > 0 then -- check to make sure the player hasn't died
                for _,Part in pairs(NoclipPart:GetTouchingParts()) do -- loop through all parts touching the NoclipPart
                    if Part:IsA("Part") and Part.Parent ~= Character and Part.CanCollide == true and not Part.Parent:FindFirstChild("Humanoid") then  -- checks to stop false flags
                        local Origin = NoclipPart.Position
                        local Direction = Part.Position

                        local RayParams = RaycastParams.new()
                        RayParams.FilterDescendantsInstances = {Character}
                        RayParams.FilterType = Enum.RaycastFilterType.Exclude -- filter out parts within the Player's Character

                        local RayResults = workspace:Raycast(Origin, Direction, RayParams) -- raycast from the NoclipPart to the touching Part

                        if not RayResults then -- if the raycast returned nil then they must be inside the part because the raycast found no faces to intersect with
                            Humanoid.Health = 0
                            warn(Player.Name,"Triggered anti noclip")
                        end
                    end
                end
            else
                break -- break out of the loop if the player has died
            end
            task.wait() -- this can be changed but teleport through parts won't be detected anymore
        end
    end)
end)