A♠Q♠ SB vs BTN, river on J♦ 8♠ 5♣ 9♠ 2♦, 60 bb

Best play: Overbet 120% pot

Why

River, J‑8‑5‑9‑2 with two spades on board (8‑9 of spades). Hero is out of position as SB and leads first. Counting suits: hero's A‑Q of spades plus only two board spades is four spades, NOT a flush; with no pair, no straight, hero has just ace-high. With essentially no showdown value, the overbet lead is a pure bluff, and the A-spade is a strong blocker that removes the nut-flush and many A-x value combos from the capped BTN, maximizing fold equity.

Key idea

Four to a flush is not a flush. With a busted ace-high holding the key suit blocker, an overbet is a pure bluff that leverages fold equity, not a value bet.

Common mistake

Miscounting four spades as a made flush and 'value' overbetting it, when the hand is actually ace-high and the size is a bluff.