It's NOT what you think. Get your head outta the gutter. SA* is an abbreviation for Second Attempt. It generally refers to a man and a women (or man) after there first round of sex. SA* is what they ask for and what they receive, but only sometimes. Another definition could be when a child asks a teacher for a SA* on their math assignment.
Man: That was good, wanna go for an SA*
Woman: Bet
Man: *fucks*
Woman: *moans*
Man: *Prematurely ejaculates*
Woman: FUCK YOU
Woman: *leaves*
Student: I didn't do well on my math assignment can I have an SA*
Teacher: Sure but not in the bedroom.