Philidor Defense

1. e4 e5 2. f3 d6
What if Black plays solidly? The Philidor Defense. Black solidly supports the pawn on e5, though now the bishop on f8 is feeling a little claustrophobic. 
3. d4
A 'pawn break.' White enjoys a slight lead in development and aims to exploit this by opening lines in the middle. 
3... g4?
Black's pawn on e5 was double attacked, and Black contrives to hold it by indirect means. 3...Bg4 creates a 'pin': White's knight cannot move since this would immediately lose White's queen. 
4. dxe5! xf3
Unfortunately forced if Black doesn't want to lose a pawn. If 4...dxe5, you may have seen 5.Qxd8+ Kxd8 6.Nxe5. 
5. xf3 dxe5
Black has won the pawn back, but 
6. c4!
Threatening mate! Black must tread cautiously. In the famous 'Opera House Game' Black did not manage to survive much longer!