Coffman's pitching ultimately drew the attention of major league scouts, and he was signed by the Detroit Tigers. In 1935, Coffman was assigned to the Charleston Senators in the Middle Atlantic League. Despite an 8–13 record in 1935, Coffman's 2.87 earned run average and his fastball showed promise. In September 1935, the Tigers announced that Coffman would report to Beaumont, Texas for the 1936 season. At the time, the "Charleston Daily Mail" summarized Coffman's performance and prospects as follows:"Coming from a southern family that has already produced one big league pitcher, Coffman has a thorough knowledge of his position. His blazing fast ball is his biggest threat and it has enabled him to strike out 161 batters this year while walking 82. While his control isn't as good as Twardy's, it is good enough considering he is a fast ball pitcher."