Chess Opening Theory/1. e4/1...e5/2. Nc3/2...Nf6/3. Bc4/3...Bb4

Black has attacked the knight on c3 to grab it later. The position stays pretty equal, but both sides should play more careful.

Common move is 4. f4 to bring out the Vienna Gambit before it gets too late.

The position looks like Ruy Lopez but in second hand.