In his first full year in the major leagues, he drew praise for his fielding and was batting .302 when he was struck by a pitched ball and sustained a broken wrist.

[5] The deal required Fort Wayne to pay $500 for Gainer and allowed Detroit to buy him back at the end of the season for the same sum.

[3] On September 26, 1910, the Tigers exercised their option to recall Gainer, though he did not appear in any games with Detroit during the 1910 season.

[1] Early in the season, one press report noted that "his fielding is making him the sensation of the American League.

"[7] The 1911 Tigers opened the season with a phenomenal 21–2 record, and manager Hughie Jennings in May 1911 credited Gainer with significantly improving the club at first base.

[9] However, on May 20, 1911, Gainer was lost to the Tigers when he was struck by a pitch thrown by Jack Coombs and sustained a broken right wrist.

[10] In late July, Gainer was cleared to play in an emergency situation,[11] but he was sidelined again in August 1911 when it was determined that a callous had formed between the bones in his wrist.

[12] In September 1911, it was reported that Gainer would probably undergo surgery and that "his injury was so bad that his arm may never get back into right condition again.

"[13] Detroit club owner Frank Navin explained the collapse of the 1911 Tigers as follows: "It was the loss of Gainer.

He gave the infield the confidence that inspired sharp and fast fielding, and made the pitching job comparatively easy.

[1] In October 1913, the Tigers had a promising young first baseman in Wally Pipp, and one newspaper reported that Gainer was "about through as a major league player.

"[22] In December 1913, Gainer wrote from his home in Elkins, West Virginia, that he may retire from baseball altogether and go into business.

In early February, he signed a three-year contract with Boston that made him one of the highest paid players in baseball.

[1] In July 1920, the Red Sox acquired Dick Hoblitzel who became the club's starting first baseman, and asked waivers on Gainer.

[34] In all, Gainer appeared in 82 games, six as an outfielder, and hit .295 with eight triples and 29 RBIs for the 1915 Red Sox team that won the World Series.

Gainer had the third highest batting average for the Red Sox — trailing only Tris Speaker and Babe Ruth.

[35] He appeared in Game 5 in the 1915 World Series, got a base hit off Eppa Rixey in the eighth inning, and scored on a Duffy Lewis home run that tied the score, with the Red Sox then winning the game on a Harry Hooper home run in the ninth inning.

[45][46] During the summer of 1918, he played for an Atlantic Fleet baseball team that included Rabbit Maranville, Whitey Witt, and Paddy Driscoll.

[48] Gainer appeared in 47 games for the Red Sox in 1919, including 15 as a starter at first base and 14 in left field.

[1] On September 30, 1922, Gainer hit a three-run home run in his final major league at bat.

[3] He spent the 1928 season as a coach and pinch-hitter for the Rochester Red Wings of the International League, compiling a .328 average in 61 at bats.

[3] In January 1930, Gainer was hired as the manager of the Fairmont Black Diamonds in the Middle Atlantic League.

[57] According to one account, he was "well liked by fans, but poor health and a seven-game losing streak discouraged him to such an extent that he gave up the reins.