So I like, made this script at midnight, and then had to re-do it because apparently some time roblox changed KeyDown to this weird key service mumbojumbo. I barely know how it works and are exhausted because a stupid person was pestering me all day.

Please do assist.

 Player = game.Players.LocalPlayer
 Humanoid = game.Players.LocalPlayer.Character.Humanoid
 Stamina = script.Parent.Value
Running = false


function Run(key)
if key.KeyCode == Enum.KeyCode.RightShift or key.KeyCode == Enum.KeyCode.RightAlt and Stamina.Value >= 0 and Humanoid.Jump == false then
	Running = true
	while Stamina.Value > 0 and Running == true and Humanoid.Jump == false do
	Humanoid.WalkSpeed = 32
	wait(0.2)
	end	
	Stop()
	
end
end


function Stop(key)
	if key.KeyCode == Enum.KeyCode.RightShift or key.KeyCode == Enum.KeyCode.RightAlt and Running == true  then
	Running = false
	Humanoid.Walkspeed = 16
	
	end
end

game:GetService("UserInputService").InputBegan:connect(Run)
game:GetService("UserInputService").InputBegan:connect(Stop)
Anonymous