Caldwell was born in Corydon, Pa., on April 26, 1888. Corydon no longer exists because in 1965 it was put under the water of the Allegheny Reservoir when the Kinzua Dam was built. He grew up and completed high school at Salamanca.
Caldwell had a 133-120 record with 184 complete games and an ERA of 3.22 while pitching for the New York Highlanders, also called the Americans and later the Yankees, from 1910 through 1918, the Boston Red Sox for part of 1919 and the Cleveland Indians from 1919 through 1921. He had 1,006 strikeouts and 21 shutouts.
He won 20 games in 1920 for the Indians. He pitched more than 300 innings in 1915 with the Yankees and worked more than 200 innings in 1911, 1914, 1917 and 1920.