Ryan Michael Castellani (born April 1, 1996) is an American professional baseball pitcher who is a free agent.

[2][3] Castellani made his professional debut that year with the Tri-City Dust Devils[4] and spent the whole season there, going 1–2 with a 3.65 ERA in ten starts.

[9] Castellani made his major league debut with the Rockies on August 8, 2020, against the Seattle Mariners, retiring the first 12 batters he faced.

[13] He spent time with the Athletics in spring training, and was optioned to minor league camp before the 2022 season began.

[17] Prior to the start of the AA season, on May 1, Castellani was traded to the Gastonia Honey Hunters of the Atlantic League of Professional Baseball in exchange for future considerations.

[20] Castellani opened two games for Team Italy in the World Baseball Classic in March 2023, with two earned runs and three strikeouts over four innings.