Los Angeles Angels pitcher Garrett Richards is the fourth pitcher this season to toss a “perfect inning.”

Richards accomplished the rare feat against the Houston Astros, Deadspin reports. The 26-year-old struck out three batters on nine pitches in the second inning of Wednesday night’s game.

The achievement, known as a “perfect” or “immaculate” inning, is usually quite rare. However, Richards is the fourth pitcher to do it this season and the second pitcher to do it this week. Cleveland Indians starter Justin Masterson managed an immaculate inning against the Boston Red Sox on Monday.

Masterson and Richards joined Philadelphia Phillies ace Cole Hamels and Tampa Bay Rays starter Brad Boxberger as the only pitchers to strike out three batters on nine batters this season. To put that number in perspective, there have never been more than four perfect innings in a single season in the history of baseball, Deadspin notes.

Furthermore, this is just the third time in history that four immaculate innings have occurred in the same season. It also happened in 1998 and 2002.

Richards is the 71st pitcher since 1889 to toss a perfect inning, according to the Baseball Almanac, which has a list of every pitcher to accomplish the feat. He struck out nine batters in eight innings of scoreless work against the Astros, earning his fifth victory of the season in the process.

Highlights from Richards’ nine-pitch, three-strikeout inning can be viewed below.