I've recently done some studying on the Philidor defence which I have poor score against. I might publish my extensive study later, but for now I want to discuss just a part of it. After 1.e4 1.e5 2.Nf3 d6 3.d4 Nd7 4.Bc4 black should respond with 4...c6. However, it's easy to play 4...Nf6? which according to my analysis gives the white two great options. (As a side note, 4...Bd7? is even worse and 4...h6? allows white to launch a brilliant attack including a bishop sacrifice on f7.)
White can play the safer 5.exd5 which wins a clear pawn. Black recaptures with the knight: 5...Nxe5. (Not with the pawn because of 5...dxe5?? 6.Ng5 and the f7 pawn cannot be defended.) Game continues 6. Nxe5 dxe5 7.Bxf7+! Kxf7 8.Qxd8 Bb4+! 9.Qd2 Bxd2 10.Nxd2 and white has clear pawn advantage.
The other, more exciting option is 5.Ng5!? Then 5...d5 is forced and we play 6.exd5. 6...Bb4+ and 6...Bd6 give the white a 0.4 advantage according to Stockfish, but let's suppose black chooses the third alternative 6...h6 which is +0.5 according to Stockfish. We could retreat with 7.Nf6 and have that slight lead, but more interesting is 7.Nxf7! The game continues 7...Kxf7 8.d6+ Kg6! (8...Ke8 9.Qd3 9...e4 10.Qg3 11.g5 dxc7 Qe7= white has three pawns for a knight) 9.Qd3 e4 10.Qg3+ Kh7 11.Bf7?! g5 dxc7 Qe7. White still has some ideas, but they are becoming more desperate.
So you can choose a safe 5.exd5 whcih gives white a clear edge or the exciting 5.Ng5!? My question is, why is EVERYONE playing the rather passive 5.Nc3? A great majority of the games in the tablebase continue 5...Be7 6.O-O O-O. The white is better, but is he better than after 10.Nxd2 in the 5.dxe5 line? I don't think so. The tablebase also tells me that by playing 5.Nc3 you lose 24 percent of games, draw 38 percent and win 38 percent of them. I'm sure that on top level white would do better than that if he is a pawn up in a peaceful position, right?
There is clearly something I don't understand. Help appreciated.