Answer:
The shorter I am the bigger I am.
Weight in my belly trees on my back nails in my ribs feet I do lack.
I am the best thing that can happen after a stick hits a ball.
No matter how little or how much you use me, you change me every month.
I can climb mountains, cross streams, handle hundreds of feet each day, yet I never move. What am I?
A leathery snake, with a stinging bite. I'll stay coiled up, unless I must fight.