He was part of a Bills' defense that did not allow a rushing touchdown for 17 consecutive games over a portion of the 1964 and 1965 seasons, winning the American Football League Championship in both years. Day said of winning the AFL championship, "Winning the championship is like making love to the most beautiful woman in the world." He was an AFL All-Star in 1965.
He played a significant role on a Bills' defense that prevented opposing teams from scoring rushing touchdowns for 17 consecutive games during parts of the 1964 and 1965 seasons, leading to their back-to-back AFL Championship wins in those years. Day expressed his feelings about winning the championship by comparing it to an experience of profound intimacy with a beautiful woman. He was recognized as an All-Star for the American Football League in 1965.