Chess Opening Theory/1. e4/1...e5/2. f4/2...exf4/3. Nf3/3...g5/4. h4/4...g4/5. Ne5/5...Nf6/6. Bc4/6...d5

White's c4-bishop and e4-pawn are forked by the Black pawn on d5. 7. exd5 is necessary to remove the threat.

7. Bxd5 would be a positional disaster for White. It would give Black a powerful centralised queen after 7...Nxd5 8.exd5 Qxd5, it would bring White no closer to recovering the pawn, and it would give up the bishop pair for no reason. In the analogous position after 7.exd5, 7...Nxd5 would not oblige White to capture the knight.