Some rabbits (females especially, and it is more common in certain breeds) can be pretty territorial of their cages. They will growl and lunge if you reach in. Dwarf breeds tend to have this behaviour more than other breeds, but any breed can have it. Spaying or neutering the rabbit often helps a lot. Also, when you take the rabbit out of the cage, offer it a treat and pet it gently on the head. Avoid touching the hind end as much as possible. That is where rabbits nip at other rabbits to tell them they are the boss (and to start fights), whereas the head is the area rabbits will groom each other to say they are friends. Teach them in this way that you are a friend and that coming out of the cage and being held is enjoyable.