A Shark is someone who is against a ship, oftentimes they later become Wrecking Balls.
A Shark is someone who is against a ship. People involved in the ship are not considered sharks whether they support it or not. A Shark may be someone who likes someone in the ship, though. A Shark usually is either anti-shipping or supports a different ship that is in opposition to that particular ship. Sharks hate it when ships sail, and sometimes try to stop the ship from setting sail or dry to make it bump into an iceberg, making them into a Wrecking Ball.