He played one game in the National Football League (NFL) for the Louisville Colonels, and later coached the Wilmington Clippers and Scranton Miners, as well as several high school teams.

[2][3] After graduating, Slagle spent time professionally with "Atlantic City, Canton [Bulldogs], New York [Giants], Chicago [Bears], Louisville [Colonels], Cincinnati, and Wilmington," according to The Tribune,[1] though his only known game in the National Football League (NFL) came in 1926 with Louisville.

The Colonels, after suffering a defeat in the first game of the season, "re-arranged" their lineup for their matchup with the Detroit Panthers, and signed several players including Slagle.

[8] In 1939, Slagle was hired as the head coach of the Scranton Miners, a team in the Eastern Pennsylvania Football League (EPFL).

[2] He accepted a position at Pottstown High School in 1940 to be head football coach and English teacher, but resigned in December that year.