Diemer-Rosenberg Attack

The Diemer-Rosenberg Attack is the Blackmar-Diemer Gambit line in which White answers 2...dxe4 with 3. Be3 rather than the standard 3. Nc3. The bishop develops at once and protects d4, which is White's only central pawn, against counterattacks on it. The cost is that the move does nothing against the e4-pawn. In the main line, 3. Nc3 attacks that pawn immediately and prepares f3. Here White first secures the center and leaves the knight's development for later, which gives Black a free hand in choosing a setup.

The usual reply is 3...Nf6, chosen in more than half of the games. It develops and adds a defender to e4. 3...Nc6 puts pressure on d4 straight away. 3...f5 props up the extra pawn in the manner of the Netherlands Variation. Engines also rate the central strike 3...e5 highly. The engine evaluation gives Black a slight advantage, a little larger than in the main gambit lines, and Black scores marginally better than White in online games. The line is a moderately rare sideline within an opening that is already offbeat.