Try this:
local Players = game:GetService("Players")
local runAnimation = Instance.new("Animation")
runAnimation.AnimationId = "rbxassetid://16754777947"
Players.PlayerAdded:Connect(function(plr)
local character = plr.Character or plr.CharacterAdded:Wait()
local humanoid = character:WaitForChild("Humanoid")
local rootPart = plr.Character:WaitForChild("HumanoidRootPart")
humanoid:GetPropertyChangedSignal("MoveDirection"):Connect(function()
print(rootPart.Velocity.Magnitude)
if rootPart.Velocity.Magnitude > 25 then
--Run Animation
local runAnimationTrack = humanoid:LoadAnimation(runAnimation)
if not runAnimationTrack.IsPlaying then
runAnimationTrack:Play(0.1)
end
end
end)
end)