Brentano Gambit

The Brentano Gambit, also called the Brentano Defense, is Black's 3...g5 against the Ruy Lopez. The idea is ...g4, driving the knight away from e5 and later storming a castled king. The critical reply is 4. d4. It opens the c1-bishop's diagonal to g5 while hitting e5, so 4...g4 runs into 5. Nxe5. Engines give White a clear advantage. Franz Brentano published analysis of the line in 1900, and Carl Schlechter tried it against Richard Teichmann in 1904.