Do zebras protect themselves by kicking out their back legs?

They do, just not as much as animals like those of the feline family would. Zebras, just like any horse, prefer to utilize the power in their hindquarters to fight than the pawing capacity of their front legs. The front feet and legs are more to block and parry with a rival stallion than to strike with. The main thing they'd use to strike with coming from their forehand (or front quarters) is their mouth.