Defending the big blind

You're in the big blind and someone opens. You have three options: re-raise (3-bet), call or fold.

The blind discount

Since you already posted a mandatory 1bb, completing costs you less. If your opponent opens to 2.5bb, you only have to pay 1.5bb more to see a flop in a pot that already holds ~5bb: you're getting excellent pot odds. That's why you defend much wider from the BB than from any other position — sometimes 40–60% of hands against a button steal.

3-bet, call or fold?

• 3-bet: your top hands (for value) + some bluffs with blockers, like A♥5♥ (the A blocks their AA/AK).
• Call: playable hands that want a cheap flop — suited connectors, medium broadways, small pairs.
• Fold: the trash with no potential, even with the discount (e.g. J♣4♦).

And you defend more the later your opponent opened: against the button (which opens loose) you fight back with tons of hands; against UTG (which opens strong) you're selective.