A perfect inning, or an immaculate inning, occurs when a pitcher strikes out all three batters he faces in one inning using the minimum possible number of pitches: nine. This feat is so rare that it has only occurred 114 times in Major League history, accomplished by 104 pitchers, with 79 being right-handed and 25 left-handed.
The Rarity of the Perfect Inning
The chance of an immaculate inning per half-inning is a minuscule 0.0026%, making it rarer than a perfect game. However, the chance of one being thrown in a game is slightly higher at 0.023%. To put this into perspective, over the 154 years of Major League Baseball history and over 235,500 games played, there have been only 24 official perfect games.
The Evolution of the Perfect Inning
Interestingly, the frequency of immaculate innings has varied widely throughout baseball history. There were only 31 immaculate innings in the 114 Major League seasons from 1876 to 1989. However, the pace picked up significantly in the following decades, with another 31 occurring in the 20 seasons from 1990 to 2009. The trend continued to accelerate, with 43 immaculate innings recorded in the 12 seasons from 2010 to 2021.
Notable Perfect Innings
Several notable pitchers have achieved this impressive feat more than once, including Hall-of-Famers Lefty Grove, Sandy Koufax, Nolan Ryan, and Randy Johnson, and active pitchers Chris Sale, Max Scherzer, and Kevin Gausman. Koufax, Sale, and Scherzer are the only pitchers to achieve an immaculate inning three times.