Flop Analysis
Checking back top pair on this monotone texture is a high-frequency play to protect our range and avoid getting blown off our equity by a check-raise.
When the board completes a flush, our hand strength is relative to our specific spade; with no spade in hand, we must fold to river aggression.
Checking back top pair on this monotone texture is a high-frequency play to protect our range and avoid getting blown off our equity by a check-raise.
Checking is mandatory here. The fourth spade makes our top pair extremely vulnerable, as any single spade in the SB's range now beats us.
Calling the river bet is a significant error. While we technically have a flush because of the five spades on board, we hold the absolute minimum strength possible.
Note: Calling with the board flush and no spade in hand is a losing play; SB's betting range is heavily weighted toward holding a single spade for a higher flush.