Slagle grew up in Baltimore, Maryland, and attended the Gilman School before enrolling at Princeton University.
After missing most of the 1926 season due to illness, Slagle left the hospital in November 1926 to lead the Tigers to their third consecutive victory over Harvard.
When you consider that previously he had played only forty minutes of football during the present season and came out of the hospital only a week ago, I think the brilliance of his performance was unbeatable.
"[12]Slagle also played soccer and baseball at Princeton and was awarded the Poe Cup in June 1927 as "the star triple threat of the Tiger eleven for the past three years.
[13] In June 1928, he returned to Baltimore and was hired as the backfield coach for the football team at his alma mater, the Gilman School.