K♦9♦ BB vs BTN, turn on Q♦ 9♣ 4♠ 2♦, 70 bb

Best play: Raise

Why

The 2♦ turn on Q♦9♣4♠ is a low brick that brings a second diamond, helping no straights but adding flush equity. As the OOP BB you hold K♦9♦ = middle pair (the 9) plus the K-high flush draw (two diamonds in hand, two on board). Facing the BTN's bet you check‑raise: this is a premium semi-bluff — you have a pair as a backup, a strong flush draw, and an overcard (K), so you raise for value-plus-equity against his wide range, generating fold equity now and stacking him when the flush or trips arrive, far better than passively calling.

Key idea

OOP with pair + strong flush draw, the check‑raise beats the call: you add fold equity now and still have the best draw when called.

Common mistake

Just calling with pair-plus-flush-draw, missing the fold equity and the chance to build the pot while you still have outs.