How do I make a backwards walking animation play on a character?

I am making a custom character for my game. I don't really care what kind of animation script I'll be using (Made by myself or the standard ROBLOX character "Animate" script).

My problem is that I need to figure out which direction the player is walking in and load the animation onto a humanoid. I've tried using vectorToObjectSpace, Humanoid.MoveDirection() and other movement tracking code, but none of it has worked. Maybe I'm doing something wrong? Please help.