Rossman finally made it to the major leagues in September 1904, playing 16 games in right field for the Naps in the closing weeks of the season.

Rossman's .308 average in 1906 was 8th best in the American League and third highest among the Cleveland regulars—trailing two Hall of Famers, Nap Lajoie and Elmer Flick.

With Ty Cobb and Sam Crawford already in the Detroit lineup, the addition of manager Hughie Jennings and Rossman in 1907 gave the Tigers the spark they needed to win three straight American League pennants from 1907 to 1909.

Rossman also excelled in the 1907 World Series, batting .474 with a .579 slugging percentage, 9 hits, 2 RBIs and a run.

Rossman was among the American League leaders in most batting categories: 2nd in doubles with 33 (trailing only Ty Cobb); 3rd in total bases with 219 and extra base hits with 48 (trailing teammates Cobb and Crawford in both categories); 4th in slugging percentage at .418; 5th in RBIs (71), triples (13), and OPS (.748); and 6th in batting average at .294.

On August 20, 1909, with Rossman batting .261 in his third season in Detroit, the Tigers traded him to the St. Louis Browns for Tom Jones.

Financial troubles were thought to be a cause of his condition;[3] it was reported that he had $20,000 saved when he last played professional baseball seven years earlier but was down to less than $100 at the time of his breakdown.

[6][7] He is buried in an unmarked grave within the Rossman family plot in the Mellenville Union Cemetery, just outside the village of Philmont.