San Francisco 49ers quarterback Alex Smith had just led his team to the NFC Championship Game when he was rattled by a concussion. Despite his promising career, Smith was immediately replaced. Sometimes all it takes is one moment of bad luck for athletes to fade into sports obscurity.

Our partners at Bleacher Report have gathered a list of the 20 unluckiest athletes of all time. Some experienced career-killing injuries; others just had a few too many run-ins with the coach.

If you think luck involves a little more than chance, you're not alone. Check out the 10 most superstitious athletes.