Green’s Dictionary of Slang

(US) to walk.

1927		T. Thursday ‘West Goes South’ in Everybody’s Oct. 🌐 A hawk-nosed gent alights from the bus, and [...] flatfoots into our office.
1930		J. Lait Gangster Girl 53: The ex-convict servant flatfooted in.
1934		(con. 1920s) J.T. Farrell Young Manhood in Studs Lonigan (1936) 161: He flatfooted along twirling his club.
1946		C.S. Montanye ‘Opals Are Unlucky’ in Thrilling Detective Jan. 🌐 The big detective [...] flatfooted it down a cement-paved aisle.