Chess Opening Theory/1. e4/1...e5/2. Nf3/2...Nc6/3. Bc4/3...Nf6/4. Ng5/4...Bc5/5. Nxf7/5...Bxf2/6. Kxf2/6...Nxe4/7. Ke3/7...Qh4/8. g3/8...Nxg3/9. hxg3/9...Qd4

9... Qd4+
Black cannot be allowed to capture the c4 bishop with check so 10. Kf3 is the only move.