A♦5♦ SB vs BTN, river on J♦ 8♠ 5♣ 9♠ 2♦, 80 bb

Best play: Check

Why

River (J‑8‑5‑9‑2). SB vs BTN, hero is out of position and leads first. Hero's 5-diamond pairs the 5 on the flop for bottom pair of fives with an ace kicker; the diamonds total only four (J‑2 of the board plus A‑5 of diamonds), so no flush completes and there are no draws on the river. Bottom pair beats only missed draws and air, so betting it for value gets called only by better and folds out worse: this is a showdown hand. A check is better than the 40% lead.

Key idea

Bottom pair on the river is a showdown hand; betting it thin only gets called by better and folds out the bluffs you beat.

Common mistake

Thin-value-betting bottom pair; on the river it has no equity to deny and beats only the hands that would fold.