to fuck a girl just for the hell of it. also look at fuck.
Guy1: Darryl shaged 3 girls so far...u think u can compete with him??
Guy2: O man dont worry I been doin ma homework on that facebook i think i can get a shag or two with these fit birds.
Guy1: get it sorted son, get it sorted!!!
Yet another definition for SHAG....in a mid 1950's Chuck Berry song (I think it was Mabellene), there's a line that goes, "shag on down to ..... ". In the context in which it's written, it means to go some where. Such as, "Let's shag", meaning, "Let's go" (rather than let's fuck).