He played in Major League Baseball as a catcher from 1939 to 1951 for the New York Yankees, Cleveland Indians, Philadelphia Athletics, and Boston Red Sox.

[2] Rosar was first discovered in 1934 when he was chosen to play in an All-Star game for amateur baseball players from Buffalo, New York.

[3] The wife of New York Yankees manager, Joe McCarthy, attended the game and was so impressed with Rosar's catching ability that she told her husband about him.

[15] With the outbreak of World War II creating doubts as to whether Major League Baseball would continue to operate during wartime, Rosar asked Yankees manager, Joe McCarthy, for permission to travel to Buffalo in July 1942 to take examinations to join the Buffalo police force and, to be with his wife who was about to have a baby.

[17] When he returned to the club three days later, he found that McCarthy had replaced him with Rollie Hemsley and sent Kearse to the minor leagues, relegating Rosar to third-string catcher.

[16] Rosar had been seen as a successor to the aging Dickey but, after flouting the authority of the Yankees management, he would be traded to the Cleveland Indians by the end of the season.

Rosar was hitting for just a .216 batting average by mid-season in 1948, but his defensive reputation won him the fans' vote as the American League's starting catcher in the 1948 All-Star Game.

[19] With the Red Sox, he was the third string catcher behind Birdie Tebbetts and Matt Batts in 1950 and then to Les Moss in 1951 before being released in October 1951.

[6] Despite his relatively low offensive statistics, Rosar's defensive skills earned him a place on the American League All-Star team five times during his career.