Facing a flop shove on KJ9r with top pair + gutshot and getting ~2.1:1, we should continue; folding is overly tight.
Flop KJ9 rainbow is very connected and favors BTN’s range, so from BB we mostly check and let BTN drive the action. With top pair + gutshot on this texture, checking is standard—our hand is strong but not invulnerable, and we don’t want to build a huge pot OOP against a range advantage.
BTN now shoves 55BB into 4.5BB, so we’re calling 52.1BB to win about 111.6BB, needing roughly 32% equity. Top pair + gutshot on KJ9r has plenty of equity versus a realistic BTN range that includes strong made hands, draws, and bluffs. Solver prefers calling here and sometimes raising as a bluff; folding is too conservative and gives up a very profitable call.
Note: Folding to the flop shove with top pair + gutshot and getting about 2.1:1 is too tight; we should continue versus a realistic BTN range.