Case Study Series: Blind Defense

The battle for blinds is at the core of online poker. Every pot begins with forced money in the middle, and how aggressively players fight for or defend it defines much of the game’s profitability. Solvers make it clear that defending blinds is essential—folding too often hands the opener free equity. Yet datamined hand histories consistently reveal that regulars, even at mid-stakes, under-defend, particularly from the small blind.

For the disciplined grinder, this tendency is gold. By adjusting open-raising frequencies based on population data, you can exploit this under-defense to build a steady profit stream without ever seeing a flop.

Step 1: What Theory Says About Blind Defense

In GTO simulations, the small blind is supposed to defend around 35–40% of hands against a button open, and the big blind closer to 55–60%. These ranges include a mix of 3-bets, calls, and folds, balancing aggression with protection. The idea is simple: if you fold too often, the button can profitably open wider and print money.

Step 2: What the Data Reveals

Datamined hand histories tell us that the population does, in fact, fold too often—especially from the small blind. Instead of defending the theoretical 35–40%, many regs defend only 25–28%. The big blind fares slightly better but still under-defends relative to solver benchmarks.

Why does this happen?

Fear of marginal spots: Defending wide from the small blind creates tough postflop scenarios out of position. Many players prefer to avoid them entirely.
Over-simplification: Some players adopt rigid strategies like “only 3-bet or fold in the small blind,” cutting out the flatting range entirely.
Variance aversion: Defending wide increases variance, and many regs value “smoother” results over maximizing expected value.

The result is a structural leak: players give up too much equity pre-flop, letting the button profit by opening more than theory prescribes.

Step 3: The Counter-Strategy

If blinds are folding too often, the adjustment is obvious: open wider from late position, particularly the button. Solvers recommend opening ~45–50% of hands from the button, but against under-defending blinds, profitable open frequencies can stretch to 55–60%.

Practical Adjustments:

Button vs. Small Blind & Big Blind: Widen opening ranges to include weaker suited kings, offsuit connectors, and even hands like 85s or Q4s that are marginal in theory but profitable against over-folding blinds.
Cutoff Exploitation: The cutoff also benefits, as players under-defend vs. CO opens as well. While theory suggests a 28–30% open frequency, you can stretch this closer to 35%.
Exploit Passivity with Small Sizings: Since your opponents are folding more often than they should, smaller open sizings (2x–2.2x) exploit them further by risking less while still forcing folds.

Step 4: A Case Study in Action

Spot: You’re on the button with 86s. Solver suggests this hand is close to the margin, opening it around 50% of the time.
Population Data: Datamined hand histories show the small blind folds ~72% of the time to button opens, and the big blind folds ~40%.
Adjustment: Open 86s every time. Even if the hand underperforms post-flop, the immediate equity gain from pre-flop folds makes it profitable.

Multiply this adjustment across thousands of hands and dozens of marginal open spots, and the EV gain becomes significant.

Step 5: Protecting Against Adaptation

Could blinds adjust and start defending more? Of course. But hand histories show this is unlikely at scale. Defending wide out of position is uncomfortable and variance-heavy, which deters many players from correcting the leak. Until they do, the exploit remains a reliable long-term edge.

Conclusion: Quiet Profits, Big Results

Targeting under-defended blinds is not flashy. You won’t be pulling off massive river bluffs or showdown hero calls. Instead, you’re picking up small, steady profits by stealing what your opponents surrender too easily.

Hand histories make the evidence undeniable: regulars don’t defend as widely as solvers dictate. By opening wider from late position, you exploit this imbalance and add consistent EV to your game. Sometimes the simplest adjustments, repeated hand after hand, create the largest long-term profits.