Sometimes my opponents choose very defensive ways of dealing with the Blackmar Diemer, for example 1.d4 d5 2.e4 dxe4 3.Nc3 Nf6 4.f3 exf3 5.Nxf3 c6 6.Bc4 e6 (diagram). This has occured several times in the last weeks. Black deliberately shuts in his lightsquared bishop and takes a very defensive stand.
In the Euwe defense, black plays e6 furst and white places his bishop on d3. In the O'Kelly, black plays c6 first and white then plays Bc4. But this system is a mixture of both.
Most lines will transpose into the Euwe defense, when white will eventually place his bishop back onto d3, but there might be following different ideas.
a/ 7...Nd5 8.Bxd5 exd5 9.Ng5 (+)
b/ 7... b5 8.Bd3 b4 9.Nxe4
...b1/ 9...Nxe4 10.Bxe4 (+=)
...b2/ 9...Nbd7 10.Bf4 (+=)
c/ 7...Nbd7 8.Qe1 (=)
d/ 7...Be7 8.Qe1 (=)
e/ 7...Bd6 8.Qe1 (=)
So white quietly gets all its pieces in an Euwe-like fashion to deliver a tremendous attack. A standard line might be : 7...Be7 8.Qe1 Nbd7 9.Bg5 0-0 10.Qh4 (diagram)
We all know that h6 in the Euwe equivalent of this position is deadly, but this is when the white bishop is on d3, now it is on c4. Does 10...h6 force white to retreat ?
f. 10...h6 11.Bxh6 gxh6 12.Qxh6 (diagram)
It seems to me that black is alive and kicking in this position ! Houdini suggests more than 5 black moves, al equal. The move 12...Nh7 even gives bnlack a small lead. Hmm, let's look at 12...Nh7 (diagram)
Only 13.Bd3 is possible but now the odd looking 13.f5 saves the day for black as 14.Qxe6+ is not sufficient for a win, eg 14...Kh7 15.Rae1 Bf6 (=)
So we see that the Euwe-O'Kelly defense is not without risk for the attacker as the standard Euwe attacking lines might fail.