[3] In 1920, he made his professional debut with the Martinsburg Mountaineers of the class-D Blue Ridge League, where he appeared in six games.

[4] His performance attracted the attention of Jack Dunn, Sr. (1872–1928), the manager/owner of the minor league Baltimore Orioles, who also discovered Babe Ruth.

Dunn acquired Grove's services by giving Martinsburg enough cash to replace their center field wall.

Grove remained in the minor leagues through 1924, as owner Jack Dunn refused several offers from the majors to acquire him.

[6] In 1927, Grove won 20 games for the first time, and a year later he tied George Pipgras for the AL lead in wins with 24.

During the Athletics' championship run, Grove led the way as the league's top pitcher, posting records of 20–6, 28–5 and 31–4.

His MVP award is the only one not enshrined in the National Baseball Hall of Fame in Cooperstown, New York, instead being housed at the George's Creek Library in Lonaconing, Maryland.

During the 1931 season, Grove tied Smokey Joe Wood's and Walter Johnson's AL record with 16 straight wins.

He was attempting to win his 17th straight decision when a rookie outfielder filling in for Al Simmons, who had the day off, committed an error that led to the only run of the game.

In 1933, Grove became the first player in Major League Baseball history to strike out five times in a nine-inning game.

[8] On December 12, 1933, team owner Connie Mack traded Grove, along with Max Bishop and Rube Walberg, to the Boston Red Sox for Bob Kline, Rabbit Warstler and $125,000.

He died in Norwalk, Ohio, of a heart attack while watching a televised baseball game at his daughter-in-law's home on May 22, 1975.

[14] In 1969, Grove was voted the left-handed starting pitcher for Major League Baseball's 100th anniversary team.

According to baseball historian Frank Russo, Grove is usually thought to be the best left-handed pitcher in the history of the American League.

[17] Russo also writes, "Normalized for league average and adjusted for home park, his 3.06 ERA is quite simply the best in baseball history.