Keen had initially accepted a position as a coach at an Arkansas school in 1937, but eventually changed his mind and signed with the
Philadelphia Eagles of the
National Football League (NFL) as an
undrafted free agent. running ability, and blocking despite his size, leading his teammates to nickname him "Rabbit." He was the smallest in the Eagles' backfield, but was still considered one of their best blockers, with
Bert Bell saying "He hits harder for his size than any man I've ever seen." Through their second-to-last game, against the
Brooklyn Dodgers, he had run 29 times for 122 yards, in addition to five
receptions for 45 yards, and three incomplete pass attempts. Through 2020, it was the 14th-longest pass ever thrown by an Eagle and the 11th-longest ever thrown against the Packers, as well as the second-longest in the NFL that season; He returned to the Eagles in 1938, and initially made the team. Soon after, he was sent to the
minor league Richmond Arrows of the
Dixie League. A
triple-threat man, Keen appeared in five games for the Arrows, missing several due to injury, and scored two touchdowns, while passing for three more. He helped the team compile a 4–3 record, placing second in the league, and at the end of the year was voted the
most valuable player in the backfield. He was also a fan favorite with the Arrows, being voted the most popular back on the team. Following the season, he signed a basketball contract with
Dr. Pepper's team in the Capital City League of the Richmond Basketball Commission, playing
guard. Keen did not play professional football afterwards, and finished his NFL career with 9–10 games played, 37 rushes for 164 yards, and five receptions for 45 yards, for a total of 209
all-purpose yards, in addition to 86 yards passing. ==Later life and death==