Folding second pair to a tiny turn probe is a massive over-fold that ignores both pot odds and range dynamics.
Flop Analysis
Checking back is a perfectly viable strategy to protect our range and realize equity with a vulnerable second pair.
**Ranges:** We have the range advantage on this Queen-high board, but 99 is a classic 'mid-strength' hand that doesn't need to push three streets of value. By checking, we keep the SB's wide range of high-card hands and small pairs in the pot.
**Sizing:** If we do choose to bet, a small sizing (33% pot) is preferred. This targets hands like 66, 88, or A-high while keeping the pot manageable if we are check-raised.
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> **Takeaway:** On dry, high-card boards, checking back mid-pairs keeps your range balanced and prevents you from being blown off your equity.
Turn Analysis
Folding here is a significant error. We are getting incredible odds against a bet that looks like a weak 'probe' or a wide semi-bluff.
**Math:** We need only 20% equity to call, and our hand has over 60% against the SB's betting range. Folding here allows the SB to profitably bluff any two cards with a tiny sizing.
**Ranges:** SB's range contains many hands we beat, including 66, 88, and now heart draws like AhXh or KhJh. Since we checked the flop, SB will lead many marginal hands and air to 'see where they are at.'
**Plan:** We must call and re-evaluate on the river. We only fold if the river is an Ace or King and the SB follows up with a large, polarized sizing.
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> **Takeaway:** Never fold second pair to a 1/4 pot bet on a brick turn; you are mathematically required to defend to prevent being exploited.
Note: Folding second pair to a tiny 25% pot bet is a massive mistake; you have the required equity to call and must defend your range.