Green’s Dictionary of Slang

bottom n.2

[? SE bottom, ‘the part of a boot or shoe below the uppers; the sole, heel, and shank’ (OED)]

(US) a (fast) runner.

[US]N.-Y. Eve. Post 29 July 2/4: Jaco took to his heels, was pursued by a possy of constables and others, but he proved himself to be the best bottom.