In baseball, striking out the side refers to when a pitcher strikes out all the batters he faces in the defensive half-inning in which he pitches.
There is no official statistic in regard to this accomplishment, though it is often noted by commentators and fans when it occurs.
There is a disagreement as to the exact definition of striking out the side.
Others believe a pitcher only has struck out the side when he has retired 3 batters in succession without allowing anyone to reach base.
The former definition is unlikely, however, given the common phrase, “(the pitcher) retired the side in order.” In theory, a pitcher can record any number of strikeouts in an inning, since it is possible for a batter to safely reach first base without recording an out if the catcher does not hold the third strike.