Honestly a leopard seal would be hard pressed to do any significant damage. The bear's fur coat, and layer of fat would protect it from any serious injuries from a bite. Polar bears are also far larger and at least on land much faster. read more
But a leopard seal could kill a polar bear because of competition, they are both highly predatory feeding on large prey items like seal. They are both of comparative size and weight. A leopard seal could easily kill a polar bear in water while a polar bear would win on land. Btw this is a leopard seal. read more
Polar Bear - Ursus maritimus The polar bear (Ursus maritimus), a bear native to the Arctic, is the apex predator within its range. Its thick blubber and fur insulate it against the cold. Its fur is hollow and translucent but usually appears as white or cream coloured, thus providing the animal with effective camouflage. read more