What is a perfect game and a no-hitter in baseball?

A no-hitter is a game in which a pitcher or pitchers complete the outing without allowing a single hit. Batters can still reach base through walks, hit batsmen, errors, or catcher's interference, and runs can even score, so a no-hitter is not necessarily a shutout. A perfect game is the stricter version: twenty-seven batters up and twenty-seven down, with nobody reaching base by any route, which requires flawless defense behind the pitcher as much as dominance from the mound. Every perfect game is by definition a no-hitter, but very few no-hitters are perfect.

The rarity is the point. There have been hundreds of no-hitters in Major League history and fewer than twenty-five perfect games, which is an extraordinarily small number across well over two hundred thousand games. Don Larsen's perfect game in the 1956 World Series remains the only one thrown in a postseason game. Combined no-hitters, in which multiple pitchers contribute, have become more common as complete games have declined with modern bullpen usage and pitch count management.

Two notable near-misses illustrate how thin the margin is. Armando Galarraga retired twenty-seven consecutive batters in 2010 but was denied a perfect game by an incorrect call at first base on the final out, an error the umpire acknowledged immediately and publicly afterward, and the two men's handling of it became better remembered than most completed perfect games. And Harvey Haddix retired thirty-six consecutive batters over twelve innings in 1959 before losing both the perfect game and the game itself in the thirteenth, a performance that under current rules is not classified as a perfect game because the definition requires the game to end with the feat intact.