Rarely seen line in the three knights opening.

I was analyzing the three knights opening 1.e4 e5 2.nf3 nc6 3.nc3 and trying to find a decent way to play for an offbeat line as black, so anything that wasnt 3...nf6.

But surprisingly the lines are  suspect. 3...bc5? falls to the thematic Nxe5 and d5. 3...bb4!? 4.nd5 bc5 5.bc4 nf6 (or d6, 6.c3) 6.c3 seems to give white a pleasant edge

i analyzed 3.g6 thinking it should be ok but some of the lines look precarious for black

i also analyzed the 3.d6 lines. Since im a bit of a fan of the old steinitz of the ruy lopez i thought i would like these lines but no

I was ready to give up until i discovered the neat idea

So thats my idea. 1.e4 e5 2.nf3 nc6 3. nc3 d6 4.d4 bd7!?

if 4.bc4 we can play 4...be7 and if 5.d4 bd7 transposes! but perhaps better are the following two sidelines

a small errata on one g6 sideline

cool themes

https://openings101.org/four-knights-game/16 here is more on 3...g6 from white perspective. Maybe you will find some interesting ideas.

UPD: https://openings101.org/four-knights-game/15 and here variations which is not 3...g6 or 3...Nf6

I don't play e4 but very interesting

I played these positions with both colors so I am hoping to learn something here.

3...g6 is "!" according to Pachman (1964) Moderne Schachtheorie Offene Spiele, pages 223-224: "Diesen alten, seinerzeit von Steinitz angewandten Zug brachte Keres zu neuem Ruhm." But Pachman concentrates mostly on 4.d4 exd4 5.Nd5 "!", as does Keres (1952) Theorie der Schacheroffnungen Erster Teil.

Notable in the 3...g6 line after 4.d4 exd4 5.Nxd4 Bg7 6.Be3 Nf6 7.Nxc6 bxc6 8.e5 is the pawn sacrifice 8...Nd5. Theory gives +/-. I haven't analyzed it carefully but the late Efim Geller played it consistently, switching from 6...d6 which has been worked out to +/-. And Paul Keres was also a practitioner of 3...g6, so there may be more here than meets the eye. Sources are Botterill/Harding (1977) The Scotch, pages 90-92 for 3...g6 in general (via 4...g6 in the Scotch), and Berdichevsky (2004) Modern Practice 1...Nc6!?, games 139-142 for 8...Nd5 in particular (via 1.e4 Nc6 2.d4 e5 3.Nf3 exd4 4.Nxd4 g6).

About 3...d6, you could check Sielecki (2018) Keep It Simple 1.e4. in chapter 4 he covers black's third move alternatives. One move he gives which you didn't is 1.e4 e5 2.Nf3 Nc6 3.Nc3 d6 4.d4 Bg4.

About the line 1.e4 e5 2.Nf3 Nc6 3.Nc3 d6 4.d4 exd4 5.Nxd4 Nf6: (a) I pretty much disagree with all your following moves for white, and I also disagree with your assessment after 9.Bd3. Via a Philidor I once had this position as black with the bishop still on c8, and didn't have any trouble equalizing. (b) For what it's worth, Sielecki recommends (via transposition) 6.Bb5 Bd7 7.Bxc6 bxc6 8.Qf3, although here I once lost from the white side versus an IM. (c) None of the above is important in practice, since white has more than one way to an edge after what amounts to 1.e4 e5 2.Nf3 Nc6 3.d4 exd4 4.Nxd4 Nf6 5.Nc3 d6?!. Usually I played 6.Be2 with the idea O-O, but sometimes I played 6.Bf4 with the idea O-O-O which is also good.

thank you for a well thought and researched post, but almost all the resources you posted are from the dinosaur age lol.

for example the pawn sac with 8...nd5 is like +2 for white.

the early bg4 lines almost never work .e4 e5 2.Nf3 Nc6 3.Nc3 d6 4.d4 Bg4. 5. bb5 exd4 6.qxd4 and now what?  nge7 for example, 7.qe3 a6 8.ba4 and then what?

i dont see any reason for giving the bishop pair for free in the last line. Also the bishop on c8 changes a lot. reason being when white gets f4 going one source of black counterplay is nd7 to allow both bf6 and possibly ne5 if white plays f4-f5 the bishop on d7 actually gets in the way and sometimes black has to actually play bc8 wasting a tempi because of it. For example,  9.bd3 0-0 10.f4 re8 11.h3 and now bc8 is the engine move because black needs nd7. the alternative i bf8 12.b3 c5 13.bb2 bc6 14.qf3 and black looks like it ran out of counterplay

RE dinosaur age -- I'm from the land before time myself.

Regarding your 4...Bd7, the following seems a reasonable way for white to play. Usually black wants to answer h2-h3 by pressuring e4, but ...Bd7 seems a little slow for that.

I woudnt play for g6 but be7, nf6 0-0. usually, black will aim for h6 nh7 (looking for bg5 or ng5), with potential for f5. 

3...Bc5 is quite playable, although Black has to be careful.

Jonathan Tait covers this in his "Disreputable Opening repertoire" book.

I have played this as white in a correspondence game against a strong opponent, and failed to achieve a meaningful advantage.

I do not like the other Black alternatives to 3...Nf6. Actually I think that I do not like 3...Bc5 either, but the move IS well playable.

The idea ...h7-h6, ...Nf6-h7 requires some care. But black's position is solid and there are other ideas.

The more I think about 4...Bd7, the more impressed I am. It's similar in nature to Caruana's 5...Qd7 in the Petroff. https://www.chessgames.com/perl/chessgame?gid=1917449 Not the first move that comes to mind, but it changes the position just enough to take the sting out of the opponent's immediate plan, without giving up any of our own ideas. And as I mentioned above, there are other followups for black, for example after 8.O-O-O, instead of 8...exd4 or 8...h6, there is also 8...a6. So indeed ...Bf8-e7 seems sounder than ...g7-g6 and ...Bf8-g7.

thank you for the kind words
btw the h6-nh7 idea was mostly for cases where white plays d5 and closes the position. its prob too slow otherwise

oh this is one line i didnt include in my analysis

this gives white a slight advantage but nothing more.