Minecraft wiki entry for Combat, associated text: When alone, polar bears are neutral in that they will attack the player if they are attacked, but they can also be immediately hostile when approached if a polar bear cub is nearby. If the cub is attacked, any adults in a 41 block cuboid area will come to its defense. Attacking the adult first when a cub is nearby will cause all adults in a 21 block cuboid to attack the player. Cubs are passive in any situation.