"impudence," 1835, back-formation from sassy. The verb is first recorded 1856, from the noun. Related: Sassed; sassing. Sass (n.) as a variant of sauce is attested from 1775.
Impudence; impertinent back talk: if this reporter was going to give her any sass (1835+)
: He kept sassing his mama till she decked him
[fr sauce, ''rude and impudent language or action'']