Walk-off

A game-ending hit or play that immediately wins the game for the home team in the bottom of the final inning, so called because the losing team simply walks off the field with no more outs left to get. A walk-off can be a home run, a single that scores the winning run, even a walk or an error, anything that ends the game the instant the winning run crosses the plate. The format is unique to baseball among major sports: because the home team bats last and the game ends the moment they take the lead, there's no equivalent of running out the clock or playing a token final possession. That structural quirk is exactly why walk-offs carry so much extra drama, the crowd erupts and the game is simply over, no review, no formality, players mobbing the plate before the ball has even finished rolling. MLB's glossary entry on walk-offs has the exact definition.