Green’s Dictionary of Slang

a highway robber, usu. on foot.

1591		Greene Second Part of Conny-Catching in Grosart (1881–3) X 77: The Trailer is one that goeth on foote, but meanely attired like some plain gran of the Countrey, walking in a pair of bootes without spurres, or else without bootes.
1608		Dekker Belman of London G2: These Traylers trot upon the hoofe, and are footemen, mean in apparell, though not meane in their theeuing trade.