It depends. Some will actually go after whales, while others prefer seals.
Killer Whales prey on Grey whales, which are quite big.
Killer Whales
Leopard seals, Killer whales, and humans prey upon seals.
Only Killer Whales (Orcas) prey on gray whales.
No animals live in Antarctica: it's too cold to support a food chain on the continent. From Seaworld, "Killer whales are top predators in the sea. Healthy adults have no natural predators, but sharks prey on older, younger, or ill killer whales."
seals or sealions
They are predators.
Hammerhead sharks do not typically eat killer whales. Killer whales, or orcas, are apex predators and are much larger and more powerful than hammerhead sharks. While hammerheads primarily feed on smaller fish, squid, and other marine animals, they are generally prey for larger predators rather than hunters of animals as formidable as killer whales.
by hidding in the water
Yes
leopard seals preys on them and their prey is fish.
Killer whales are top predators in the sea. Healthy adults have no natural predators, but sharks prey on older, younger, or ill killer whales.