If you suspect that a fawn (or any deer) has been injured, do not attempt to move it. If you see an adult deer with a broken leg or other injury, leave the animal alone unless it can't stand up. Even though the injury may take a long time to heal, this is far preferable to the trauma of chase and capture. Wild animals' ability to heal and their adaptability of some injuries are quite amazing. If in doubt, call the police or rehabilitator.