Mars
The division means the ligue which your bunny will run.
You know, there are the stars (blue or yellow) bellow your bunnies.
For exemple you have a bunny with two stars ; he is in division 2. He'll run with bunny who got a specific potential (which include stamina, speed and acceleration) and the further you up the divisions it is most hard.
I hope you had understand me. Tell me if not.