Part: Part Five - Betting Before the Flop

Out of the small blind

Pre-flop
Blinds 100 / 200Pot 800 (4 BB)SBA9 25,000 (125 BB)YOUto actBTN 25,000 (125 BB)Buttonraises 500 (2.5 BB)BB 25,000 (125 BB)yet to actD

A button player opens to 500 to steal. It folds to you in the small blind with A♣9♦, and the big blind is still behind you.

Button steals; you hold A♣9♦ in the small blind. Best?

WhyFrom the small blind you're committing to play the whole hand out of position, and the big blind behind can still wake up and squeeze - flatting invites the one scenario you least want. Against a button stealing wide, A-9 offsuit is plenty to re-raise: you fold out his air and take the lead in the hands that continue.
What happensBoth fold and you claim it before the flop. Re-stealing beats calling here not because A-9 is strong, but because it turns a bad seat into an initiative you controlled.
In the small blind the flat-call is the trap - you'd play out of position with the big blind still lurking. Three-bet the button's wide steal or fold the trash; re-stealing keeps you from bleeding chips from the worst seat at the table.

Out of the small blind you're stuck out of position with a live big blind still behind - so raise or fold, but don't flat and lock yourself into the worst seat.