Green’s Dictionary of Slang

a highwayman.

1608		Dekker Belman of London H2: Some of these Boot-halers, are called Termers, and they plie Westminster Hall.
1611		Middleton & Dekker Roaring Girle V i: My own father, Dapper Sir Davy, laid these London boot-halers, the catchpolls, in ambush to set upon me.
1687		J. Phillips [trans.] Cervantes Don Quixote 567: [T]he Boothalers return’d with their Prize, Two Gentlemen well mounted, Two Pilgrims a foot, and a Coach wherein there were certain Ladies.
1822		R. Nares Gloss. (1888) I 95: boot-haler. A robber or freebooter. From boot, profit or booty, and to hale, to draw away; a rascal.