The amazing feat was accomplished by Charles "Old Hoss" Radbourn during the 1884 season, when he pitched for the Providence Grays. In 1884, the Grays were then part of the National League, which, at the time, had teams in Boston, Hartford, Louisville, as well as teams that are today the Chicago Cubs, Atlanta Braves, Philadelphia Phillies, and San Francisco Giants.

Radbourn had a staggering season- going 59-12 with a 1.38 ERA, completing all 73 games he started, and had 441 strikeouts in a whopping 678 2/3 innings pitched.

More Info: en.wikipedia.org