nail-biter (n.)

"worrisome or suspenseful experience," by 1999, perhaps originally in reference to close games in sports, from the notion of biting one's fingernails as a sign of anxiety (attested from 1570s); see nail (n.) + bite (v.). Nail-biting (n.) is from 1805; nail-biter as "person who habitually or compulsively bites his fingernails" is by 1856.