?! Better is the developing move 4 Nf3, attacking Black's central pawn P/e5 - as the opening theory suggests.
4... d5 5. exd5 cxd5 6. Bc4b5
?! Better was 6 Ba2, keeping the pressure on the pawn P/d5. Note that the move 6 Bb5?! also makes it questionable what was the purpose of the move 4 a3.
6... Nb8c6 7. Nb1c3 d4 8. Bb5xc6
Not 8 Ne4?? Qa5+ and Black wins a piece.
8... bxc6 9. Nc3e4
?! Better was 9 Nce2.
9... Nf6xe4 10. dxe4 Bc8a6
! Now, White has temporary problems with castling.
After 11 Ne2 White can castle, but the Knight N/e2 remains pinned and attackable.
Black has a very good position.
?! Better was 12 c3 Qb6 13 Qc2 0-0 14 c4.
12... O-O 13. c3 Rf8e8 14. Qd1c2 Qd8b6
?! 14...c5 was stronger.
15. c4 Ra8b8 16. b4
White has managed to defend one's queenside pawns and block the diagonal a6-f1. Now, White is ready to castle or play the fork c4-c5. However, Black has a strong centre, a bishop pair and a lead in development.