Why does Animation still play when I am standing completely still?

So I've loaded an animation onto my character and I want it to play when I am "Sprinting"(when I press LeftControl), but the animation still plays when I am standing still. How do I stop the animation when I am standing completely still? Do I have to play an idle animation?

Script:

local uis = game:GetService("UserInputService")
local Player = game.Players.LocalPlayer
local Character = Player.Character
local sprinting = false
local anim = Instance.new("Animation")
anim.AnimationId = "http://www.roblox.com/Asset?ID=4835831357"
PlayAnim = Player.Character.Humanoid:LoadAnimation(anim)

uis.InputBegan:Connect(function(key, processed)
    if processed then return end 
    if key.KeyCode == Enum.KeyCode.LeftControl and not sprinting then
		sprinting = true
		script.Parent.Humanoid.WalkSpeed = 26
		PlayAnim:Play()
		
	elseif key.KeyCode == Enum.KeyCode.LeftControl and sprinting then
		sprinting = false 
		script.Parent.Humanoid.WalkSpeed = 16
		PlayAnim:Stop()
	end
end)

You have to stop the animation using animTrack:Stop() when the player stops sprinting. You have to also adjust the speed of your animation manually using animTrack:AdjustSpeed(x) where x is the percentage speed of the animation, e.g. when x = 1, the animation speed will be normal, and when x = 2, the animation speed will be twice as fast.

Here's the wiki link on AdjustSpeed: https://developer.roblox.com/en-us/api-reference/function/AnimationTrack/AdjustSpeed