In 1937, Coffman attended spring training with the Tigers, and as he later recalled, "this time I intended to stay with the big club." During the 1937 spring training sessions, he developed a "reputation of being a big talker and a fierce competitor." On the trip to Detroit following spring training, the Tigers played an exhibition game in Cincinnati. Coffman combined with All-Stars Schoolboy Rowe and Tommy Bridges for a shutout. Despite his performance against Cincinnati, Detroit manager Mickey Cochrane told him after the game, "We are sending you to Toledo." After unsuccessfully arguing that he had earned a spot on the Tigers' roster, Coffman told Cochrane, "I'll go to Toledo, but mark my word, I'll be back up in less than 30 days." At Toledo, Coffman won six games for the Mud Hens, leading the "Toledo Blade" to report: "This 21-year-old right-handed pitcher of the Toledo Mud Hens is proving one of the sensations of the season in the American Association.""