21

In a standard baseball game, you get 3 outs per inning for a total of 27 outs through a 9 inning game.  There have been 20 pitchers who have retired all 27 batters without allowing a base runner by a hit, a walk, or an error.  That's called a perfect game.

Until today.

Philip Humber, of the Chicago White Sox, retired 27 hitters in a row in Seattle to beat the Mariners 4-0 and become the 21st MLB pitcher to throw a perfect game.  He is the third White Sox pitcher to do so.

Well done!