How would I make the animation play only when moving?

Hi I need help with this running script Right now it plays when you press shift even if you're standing still how would you make it so it only plays it when you are moving around and stuff?

repeat
    wait()
until game.Players.LocalPlayer

player = game.Players.LocalPlayer
character = player.Character
game.Workspace:WaitForChild(game.Players.LocalPlayer.Name)
if not character then
    character = player.CharacterAdded:wait()
end

Mouse = player:GetMouse()
humanoid = character:WaitForChild("Humanoid")
s = humanoid:LoadAnimation(script.Animation)

Mouse.KeyDown:connect(function(key)
    for i, v in pairs(game.Players:GetChildren()) do
    if Enum.KeyCode.LeftShift then
            s:Play()
            humanoid.WalkSpeed = 30
        end
Mouse.KeyUp:connect(function(key)
    if Enum.KeyCode.LeftShift then
            s:Stop()
            humanoid.WalkSpeed = 16
end 
end)
end
end)