4. ...  KtxP

Black can, of course, develop his B-B4.  Then he must either submit to the Max Lange attack (5.  P-Q4, PxP) or play BxP, giving up the useful B, in which case he loses the pawn gained after 6.  KtxB, KtxKt; 7.  P-KB4, P-Q3; 8.  PxP, PxP; 9.  B-KKt5, and eventually Q-B3.

          5.  P-Q4

R-K1 at once would lead to nothing.

5. ...  PxP 6.  R-K1 P-Q4 7.  BxP!  QxB 8.  Kt-B3

---------------------------------------
8 | #R |    | #B |    | #K | #B |    | #R |
|---------------------------------------|
7 | #P | #P | #P |    |    | #P | #P | #P |
|---------------------------------------|
6 |    |    | #Kt|    |    |    |    |    |
|---------------------------------------|
5 |    |    |    | #Q |    |    |    |    |
|---------------------------------------|
4 |    |    |    | #P | #Kt|    |    |    |
|---------------------------------------|
3 |    |    | ^Kt|    |    | ^Kt|    |    |
|---------------------------------------|
2 | ^P | ^P | ^P |    |    | ^P | ^P | ^P |
|---------------------------------------|
1 | ^R |    | ^B | ^Q | ^R |    | ^K |    |
---------------------------------------
A    B    C    D    E    F    G    H

Diag. 112

This attack has been analysed extensively by Steinitz.  The only square where the Queen cannot be attacked at once by the minor pieces is at QI.  After 8. ...  Q-QI, Black obtains quite a satisfactory game:  9.  RxKtch, B-K2; 10.  KtxP, P-B4.  This is Pillsbury’s move, intending to displace the Rook.  Black has then open lines for his two Bishops as compensation for his shattered pawn position. 11.  R-KB4, Castles; 12.  KtxKt, QxQch; 13.  KtxQ, PxKt.  Now it is not easy to find a reasonable plan for White, as Black threatens to cramp White’s game with B-Q3 and P-B5.  It is therefore necessary for White to take measures against that by playing R-B4 and B-B4.  If Black still plays B-Q3, B-B4 follows, with the intention of exchanging and of provoking Black’s P-B4, which leaves the QP “backward.”

8. ...  Q-KR4
9.  KtxKt B-K2
10.  B-Kt5 B-K3
11.  BxB KtxB
12.  Kt-Kt3 Q-R3
13.  QxP Castles KR
14.  QR-Q1

Now White is ahead with his development, having both Rooks in play and his Queen better placed.  Nor can the latter be attacked by R-Q1, as White would simply play QxR.  On the Queen being driven away by the Black Knight, he exchanges the latter and plays the Queen back into the same dominating position, eventually producing a dislocation of the Black Queen’s side pawns.