Years with Boston: 1934-1941 (105-62, 3.34 ERA, 1,539.2 innings, 743 strikeouts, 447 walks)
Best Year in Boston: 1935 (20-12, 2.70 ERA, 273 innings, 121 strikeouts, 65 walks)
1934 was something of a lost season for Grove as he dealt with some injuries and only pitched in 22 games, going 8-8 with a 6.50 ERA. For that season, it appeared as if the A's were smart to deal Grove. But then came 1935. Grove had his best season for his time with the Red Sox, winning 20 games for the eighth time in his career and leading the league in ERA with a 2.70 mark. It was the sixth time he lead the league in ERA. He was also named to his second All Star team and garnered some MVP consideration.
Grove continued to pitch at a high level for the next four years. He was named to the All Star team each of the next four seasons and lead the league in ERA three times, while compiling an impressive record each season. He never again won 20 games, but he came close. He was the undisputed ace of the Red Sox staff despite nearing 40 years old.
As Grove continued to age, his eyesight started to cause some issues. He began to decline in 1940, only finishing with a record of 7-6 with a 3.99 ERA. The next season he continued to decline. He held on just long enough to win the 300th game of his career and retired shortly thereafter.
Grove sports a Red Sox cap on his Hall of Fame plaque. It is not entirely unwarranted, but he was a better pitcher for the A's. It is likely that Grove was angry with Connie Mack and the A's and chose to represent the Red Sox on his plaque.