Crocomire doesn't attack you if you don't attack him. Even if you hurt him once, he takes a few swipes at you, but doesn't charge. Crocomire is really a peaceful creature and just wants you to leave.
Even more so, Mother Brain may have left Crocomire inside one of the only rooms in Upper Norfair where the lava from Lower Norfair is visible. And even more horror: Crocomire would have survived the Ring Out if the lava was from Upper Norfair and not from Lower Norfair.