Kelly threw and batted right-handed, and was listed as a lanky 6 feet 4 inches (1.93 m) tall—the source of his nicknames—and 190 pounds (86 kg).

However, his selection is regarded as controversial, as many believe he was undeserving of the recognition and was only elected by the Veterans Committee because it consisted of his former teammates.

He was selected off waivers by the Pittsburgh Pirates on July 25, 1917, to back up Honus Wagner, but did not hit sufficiently.

[1] The Giants optioned Kelly to the Rochester Hustlers of the Class-AA International League, where he played the rest of the 1917 season.

[1] He opened the 1921 season with at least one hit and one RBI in eight consecutive games, a record that stood until it was broken by Jorge Cantú in 2010.

Kelly set a National League record with seven home runs in six consecutive games in 1924, which has since been matched by Graig Nettles, Walker Cooper, and Willie Mays.

[11] In the final series of the 1924 season, the Giants were playing the Philadelphia Phillies at the Polo Grounds and battling for the pennant with the Brooklyn Dodgers.

It eventually led to the lifetime suspension of O'Connell and Giants coach Cozy Dolan by Commissioner Kenesaw Mountain Landis.

[13] That following offseason, Kelly, Sam Bohne, and other Major League Baseball (MLB) players agreed to play professional basketball with O'Connell.

[14] National League (NL) president John Heydler insisted that anyone who played with O'Connell could be suspended.

[20] Kelly was released by the Reds on July 10, 1930, and signed by the minor-league Minneapolis Millers of the Class-AA American Association.

[1] The Millers traded Kelly to the Chicago Cubs for Mal Moss and a player to be named later (Chick Tolson) late in the 1930 season to fill in for the injured Charlie Grimm.

[1] He returned to the Millers for the 1931 season, and participated in a tour of Japan along with Frisch, Lou Gehrig, Mickey Cochrane, Al Simmons, Lefty Grove, and Rabbit Maranville, among others.

His positioning and footwork on hits to the outfield became the standard method for teaching future first basemen to handle relays.

[5] When Kelly was elected, the Veterans Committee included two of his former teammates, Bill Terry and Frankie Frisch, who also shepherded the selections of teammates Jesse Haines in 1970, Dave Bancroft and Chick Hafey in 1971, Ross Youngs in 1972, Jim Bottomley in 1974, and Freddie Lindstrom in 1976.