He played in Major League Baseball (MLB) before and after World War II for the Brooklyn Dodgers and New York Giants.

Rosen turned professional in 1931, signing a contract with the Rochester Red Wings of the International League, but did not stick with the team.

[5] When Grimes joined the Brooklyn Dodgers in 1937, he convinced the team to acquire Rosen in August for $10,000 ($212,000 today) and a player.

[5] He then joined the Syracuse Chiefs of the International League, playing there from 1940 until being re-acquired by the Dodgers during the 1944 season in exchange for Bill Lohrman and Fritz Ostermueller.

He was named manager of the Ontario all-star team that played the Intercounty Maple Leafs in an exhibition game in August.

[9] He was also a business executive with a major Canadian brewery, John Labatt Limited, in their sales staff and was still so popular in baseball circles he was answering around 2,000 pieces of fan mail annually in his later years.

[11] He died of pneumonia in Toronto's Sunnybrook Hospital on April 6, 1994, at age 81 and was buried at Beth Tzedec Memorial Park.

[14] He held the distinction of being the only Jewish-Canadian major leaguer for almost 70 years until London, Ontario-born Adam Stern suited up for the Boston Red Sox.