The Red Sox signed Thomas in 1911 but allowed him to play the 1911 season with the Sacramento Sacts before recalling him to the Major Leagues for the 1912 season.[1] He spent the 1912 season as a little-used backup catcher for 1912 World Series championship Red Sox.[1]
A fine defensive replacement, Thomas was the primary catcher for the Red Sox during three years, helping them to the World Championship in 1915 and 1916. On June 23, 1917, Thomas was involved in a combined no-hitter in which he and Babe Ruth were both ejected after disagreement over the strike zone after Ruth walked the first batter. Ernie Shore and Sam Agnew replaced Ruth and Thomas respectively and promptly caught the walked batter at second and recorded 26 consecutive outs.
In a 10-season career, Thomas was a .237 hitter (245-for-1035) with two home runs and 102 RBI, including 88 runs, 27 doubles, eight triples, 12 stolen bases, and a .318 on-base percentage. In 423 catching appearances, he committed 52 errors in 1,948 chances for a .973 fielding percentage. He appeared as himself in the Paramount feature film Warming Up.