Overview

A strikeout is a defensive play in which a batter accumulates three strikes during a single plate appearance, ending that batter's turn at the plate. It is a primary way batters are retired in both baseball and softball. In scorekeeping and statistics the outcome is commonly recorded as SO or the single-letter symbol K.

Common forms

Not all strikeouts look the same. Broadly they fall into two categories:

  • Swinging strikeout — the batter swings at a pitch and misses for the third strike.
  • Called (looking) strikeout — the umpire calls the third strike without a swing.

Scorekeepers sometimes use a backward K to indicate a called third strike and a forward K for a swinging one. The term "strikes" and the sequence that leads to three are standard parts of the game rules; see strikes for the formal definitions and behavior.

Rules and exceptions

A strikeout normally records an out, credited to the pitcher and scored against the batter. There is an important exception: if the catcher fails to catch the third strike cleanly, the batter may attempt to run to first base under specified conditions. This "dropped third strike" rule can convert what would have been a simple out into a fielder's play and possible safe call, affecting the inning's continuation and scoring.

History and notation

The single-letter K used to denote a strikeout dates back to 19th-century scorekeeping and is commonly attributed to early sports writers and statisticians who standardized shorthand for game accounts. Over time K and SO became standard abbreviations in box scores and statistical summaries. The convention persists in modern record-keeping and broadcast graphics.

Strikeouts are an important measure of pitching effectiveness and are tracked for both pitchers and hitters. While a high strikeout total often signals pitcher dominance, they also reflect changes in player approach, equipment and strategy across eras. Strikeouts can leave runners stranded and influence game strategy, substitutions and managerial decisions during an at-bat or an inning; for further context about a player's current plate appearance see at bat.