Green’s Dictionary of Slang

supporters n.

the legs.

1696		Granville She-Gallants I:1: Ang. And then my Legs, Constantia. Cons. 'Tis true, the Ladies love good Supporters—They'll do, they'll do, 'Sbud fear nothing.
1833		Bell’s Life in London 7 Apr. 3/2: Lenney [...] was once more tumbled off his supporters with a flush hit on his pudding trap.