Willett was among the most powerful men on the mound but was careless about keeping in shape. After two inauspicious trials, Willett was having his first good season in 1908 when he suffered an ankle injury; he finished 15-8, 2.28 nonetheless, helping the Tigers to their second of three straight AL flags. The following season (1909) was his best, as he went 21-10 with a 2.34 ERA and finished third in the league in wins and fifth in winning percentage (.677). He was effective in limited bullpen use in Detroit’s losing WS effort.
Willett won 59 games over the next four seasons for the Tigers, then jumped to the Federal League in 1914 and was one of the few players to see his effectiveness diminish in the new league. He was 4-16 for the last-place St. Louis Terriers and didn’t finish the 1915 season, his last. He was the second AL pitcher to hit two HR in a game (6/30/12).