William Michael Smith (born July 10, 1989) is an American professional baseball relief pitcher who is a free agent.

He has played in Major League Baseball (MLB) for the Kansas City Royals, Milwaukee Brewers, San Francisco Giants, Atlanta Braves, Houston Astros, and Texas Rangers.

[2] Making his professional debut with the Orem Owlz of the Rookie-level Pioneer League, Smith recorded 76 strikeouts while walking only six batters.

[3] On July 23, 2010, the Angels traded Smith along with Sean O'Sullivan to the Kansas City Royals for Alberto Callaspo.

[5] Smith began the 2012 season with the Omaha Storm Chasers of the Class AAA Pacific Coast League.

[14] By the end of the month of July, Smith had appeared in 27 games for Milwaukee, serving as the set-up man.

On August 1, 2016, the Brewers traded Smith to the San Francisco Giants for Phil Bickford and Andrew Susac.

[17] On March 24, it was reported that Smith elected to have Tommy John surgery on his elbow, ending his 2017 season with the Giants.

[19] On November 14, 2019, Smith signed a three-year contract with the Atlanta Braves worth $39 million, with a club option for a fourth year.

Smith closed out Game 6 of the World Series versus the Houston Astros, which Atlanta won to clinch the title.

[25] Smith made his Astros debut the following day versus the Boston Red Sox, allowing a solo home run in an otherwise clean ninth inning.

This marked Smith's third straight World Series appearance with three different teams, a feat accomplished previously by Don Baylor and Eric Hinske.

[32] Seeking to address bullpen issues, the Royals reunited with Smith and signed him to a one-year $5 million contract on December 11, 2023.

[33] Smith served as a veteran leader that could lead younger arms in the bullpen and helped recruit other free agents to the Royals.