Wilfred Charles "Sonny" Siebert (born January 14, 1937) is an American former Major League Baseball right-handed pitcher from 1964 to 1975.

He played on the 1958 team that lost in the College World Series (CWS) finals in 12 innings to the University of Southern California (whose roster included, among others, future major league players Don Buford and Ron Fairly, and major league hall of fame executive Pat Gillick[1]).

His father had been a hard throwing pitcher as a young man and injured his arm preparing for a major league tryout, losing the opportunity to audition for Rogers Hornsby and the St. Louis Cardinals years earlier.

[5] In those years with Cleveland, the starting pitching staff also included lifetime 229 game winner and hall of fame candidate Luis Tiant[10][11] and "Sudden" Sam McDowell, who was considered to be the most talented pitcher in baseball (though not the winningest).

[8] He was traded along with Joe Azcue and Vicente Romo from the Indians to the Boston Red Sox for Ken Harrelson, Dick Ellsworth, and Juan Pizarro on April 19, 1969.

[19] Siebert was the most recent American League pitcher to hit two home runs in one game, until July 27, 2023, when Shohei Ohtani matched him.

[2][20] Siebert accomplished the feat for the Red Sox on September 2, 1971, against the Baltimore Orioles, before the introduction of the designated hitter.

[21] He was traded in 1973 to the Texas Rangers, and then played for the St. Louis Cardinals, San Diego Padres, and Oakland Athletics.

[23] He was involved in a three-team deal on November 18, 1974, in which he was dealt along with Alan Foster and Rich Folkers from the Cardinals to the Padres for Ed Brinkman who had been sent to San Diego with Bob Strampe and Dick Sharon from the Detroit Tigers for Nate Colbert.