Chess Opening Theory/1. e4/1...e5/2. d4/2...exd4/3. c3/3...dxc3/4. Bc4/4...cxb2/5. Bxb2/5...Nf6/6. e5/6...d5/7. exf6

= Danish Gambit Accepted, Classical Defence =

7. exf6
Black will lose castling rights and have to play around a protected White pawn on g7 if she captures on c4 immediately.

So instead she throws in 7...Bb4+. In responding to the check, White must either give up the dark-squared bishop, block the dark-squared bishop's diagonal, block the d-file, or forfeit castling rights herself. All of those are good things for Black!