What is a Strikeout
When a batter accumulates three strikes during their at-bat and is out.
A strikeout occurs when a batter accumulates three strikes during their at-bat, resulting in an out. It is one of the most common outcomes of a plate appearance and a primary goal for any pitcher. For hitters, avoiding a strikeout — and making contact with the ball — is a fundamental objective.
How a Strikeout Works
A strike is recorded against a batter when they:
- Swing and miss a pitch entirely (swinging strike)
- Fail to swing at a pitch that passes through the strike zone (called strike)
- Foul off a pitch (counts as a strike, but cannot record the third strike on a foul ball, except for a foul tip caught by the catcher)
When a batter reaches three strikes, they are retired — recorded as a strikeout. The pitcher is credited with a strikeout (K), and the batter is charged with a strikeout at-bat.
The Letter K
Baseball uses the letter K to denote a strikeout on a scorecard. The convention dates back to the 19th century, credited to baseball statistician Henry Chadwick, who chose K because it was the most prominent letter in "struck." A backwards K (ꓘ) indicates a called strikeout — where the batter did not swing at the third strike.
Types of Strikeouts
- Swinging strikeout — The batter swings and misses the third strike.
- Called strikeout — The batter does not swing at a pitch that the umpire rules a strike.
- Strikeout looking — Another term for a called strikeout.
Strikeout Records
Strikeouts have become increasingly common in modern baseball. Nolan Ryan holds the all-time MLB career strikeout record with 5,714 Ks. In a single season, Matt Kilroy struck out 513 batters in 1886 under older rules; in the modern era, Randy Johnson (372 in 2001) stands near the top.
For batters, Adam Dunn and Mark Reynolds are among the all-time single-season leaders in strikeouts, each exceeding 200 in a season.
Strikeouts in Strategy
Pitchers aim to accumulate strikeouts because they are the most reliable way to record an out — no fielder involvement means no chance of an error. High-strikeout pitchers ("power pitchers") are especially valuable in high-leverage situations. This is why teams prize strikeout arms in their bullpen — a closer or setup man who can rack up strikeouts gives managers far more confidence when protecting a late-game lead.
For hitters, strikeouts are often considered the worst possible outcome since they guarantee no opportunity to reach base on a fielder's error or advance runners. However, modern analytics have softened this view — a strikeout is only marginally worse than a routine groundout in terms of run value.