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Preflop & Blind Defense

The preflop decisions that come up most — and the math behind them.

Why the Big Blind defends so wide

The BB defends a huge range vs a steal for two structural reasons: it has already posted the blind (a price discount) and it closes the action (no one can re-raise behind).

Example — $1/$2, 100bb, vs a 2.5x button open: the BB defends ~51.7% of hands, continuing down to ~K7o/Q8o.

Pot odds: a 2.5bb open means the BB calls 1.5 into a 4bb pot = 2.67:1 = only ~27% break-even equity (≈28.6% after rake).

But equity ≠ what you can call

That ~27% pot-odds number understates the real bar, because the BB realizes equity poorly out of position (low EQR). So the actual defending range is tighter than raw pot odds suggest — you need hands that can actually realize their equity OOP, not just clear the 27% line.

Small Blind: 3-bet-or-fold

In raked games, play the SB almost always as 3-bet-or-fold (no flatting range). Why: - A flatting range is capped (middling pairs, offsuit broadways, suited wheel aces) and gets squeezed relentlessly by the BB. - A wide flat can't beat the rake, and the SB doesn't close the action — flatting invites a multiway pot from the worst seat. - Flatting only becomes viable in unraked games (where the flat range is very wide) or vs weak/passive players.

Limping & the limp-reraise

  • Open-raising > open-limping as a rule (generates fold equity, builds value, avoids a capped/face-up range, reduces multiway pots). Narrow exceptions: loose-passive games, SB completes, some speculative hands.
  • Limp-reraise = a trap: limp to look weak, induce a raise, then re-raise. Best from early position (UTG) with premiums (AA/KK/QQ, sometimes AK) when aggressive players sit behind.

Set-mining

Calling a raise with a small pocket pair to flop a set: - You flop a set (or better) ~11.8% of the time — about 1 in 8.5 (~7.5:1 against). You miss ~88%. - Implied-odds rule of thumb: you want effective stacks ≈ 10–20× the call behind: - ~8× = bare break-even · 10× = loose floor · 12–15× = conservative. - The "5–10 rule" / "Call-20": risk ≤5% of your stack (up to 10% in special cases) — i.e. need ~20× — is the standard safe figure. - Modern solver-era theory trends higher (15×+) because you win a smaller fraction of stacks than old literature assumed.

Key takeaway

Defend the BB wide but realistically (EQR, not just pot odds); play the SB as 3-bet-or-fold in raked games; raise rather than limp (save the limp-reraise for premiums in EP); and set-mine only with ~15–20× behind.

Sources: BB defense · SB preflop · Limp-reraise · Set-mining · Flop odds