Animation on Keydown?

So what you have to do it the following ~Make your keydown function

function onKeyDown(key)
    local Key = key:lower()
    if key == "r"  then

 --  (this is a localscript in the startergui by the way)

    end
end

Next what you want to do is to define your animations

local SprintAnim = Instance.new("Animation")
SprintAnim.AnimationId = "rbxassetid://425082298" -- Or whatever your animation is

Then when you want to play that animation you do this

mouse = Player:GetMouse() -- Get players Mouse
Player = game.Players.LocalPlayer
Character = Player.Character or Player.CharacterAdded:wait()
Humanoid = Character:WaitForChild('Humanoid')

local animationTrack = Humanoid:LoadAnimation(SprintAnim)
animationTrack:Play()

Now we put it together, your results are...

Player = game.Players.LocalPlayer
Character = Player.Character or Player.CharacterAdded:wait()
Humanoid = Character:WaitForChild('Humanoid')
local SprintAnim = Instance.new("Animation")
SprintAnim.AnimationId = "rbxassetid://425082298" -- Or whatever your animation is

function onKeyDown(key)
    local Key = key:lower()
    if key == "r"  then
        game.Players.LocalPlayer.Character.Humanoid.WalkSpeed = 16 * 2.5
        local animationTrack = Humanoid:LoadAnimation(SprintAnim)
        animationTrack:Play()
    end
end 


mouse.KeyDown:connect(onKeyDown) -- Call the function c:

HOPE THIS HELPED :D