Popov Attack

does anyone have a reference concerning Popov?

There was an article in SOS 9 by Jeroen Bosch, but I dont know if it is still available. Maybe on second hand market.

Dead forum, I know, but I'm interested in the subject matter.

3... a5 actually looks quite interesting. Obviously 4. Bxc6 and the game is well and truly equal, but who would play such a horrendous-looking move?
4. c3?! and Black has chances with 4... f5!, as White's best anti-Jaenisch line (4. d3 fxe4 5. dxe4 Nf6 6. 0-0 Bc5 7. Bxc6 bxc6 8. Nxe5 0-0 9. Nc3, with a pawn up and strong center control) doesn't work, as the c3 pawn blocks the knight's natural development, and while White can do something similar with Nd2, suddenly ...d5 is in the cards for Black, and this crucial break positions Black well to set up for an equal endgame.
4. d3 and 4. 0-0 lead to similar positions where Black transitions into a Bird's Defense, except that 3... a5 functions as a rather flexible waiting move as White can't really commit to anything too hard without Black being able to structurally adapt while also having solid practical applications, allowing Black to harass the LSB and regain tempi from White's suddenly somewhat misplaced LSB.

After 3...a5, the best move is just to keep development with 4 0-0. 4 Nc3?! oddly enough gives Black an improved version of the 3...Nd4 variation of the Ruy lopez that sometimes seems GM play, so that can't be recommended. And 4 c3?! f5 allows a strange variant of the schliemann where c3 isn't exactly useful for White (as he should be playing 4 Nc3 and 4 d3 in the main lines).

Then, someone's suggestion of 4...Na7 after 4. 0-0 is awful. White can either gain space with 5 a4 Nxb5 6 axb5 followed by 7 d4 and the b5 pawn cramps Black and isn't weak at all, or White can play 5 Bc4 with a nice advantage (5 ...b5 6 Be2 d6 7 d4+/- or 6...Nf6 7 a4! b4 8 Nxe5, or 7...Nxe4 8 axb5 and Black's position is a wreck. You can't play lines like this and hope to win games.

So after 4 0-0, Black's best is to transpose into a slightly offbeat (but maybe not much worse ) form of the ...Nd4 variation with 4...Nd4, then White can choose 5 a4, 5 Bc4 or 5 Nxd4 exd4 6 Bc4, followed if necessary by 7 a4 (if Black tries ...c6). Black has a very long route to equality, and at the weaker levels, is going to struggle. You're best off just playing 3...Nd4 right away, or sticking to the main lines of the Ruy or Berlin.