There must be something else wrong with your code or animation, I did this in my own testing place and it works fine.
local Tool = script.Parent
local Player = game.Players.LocalPlayer
Tool.Equipped:Connect(function()
Player.Character.Humanoid.Animator:LoadAnimation(script.Parent.Handle.Animation):Play()
end)
Ensure that you’ve set the animation’s priority, you probably want to use “Action”. And also that you’re using the correct avatar, if the animation is for an R15 Rig it will not play while you’re using R6.