Chess Opening Theory/1. e4/1...c5/2. Nf3/2...Nc6/3. d4/3...cxd4/4. Nxd4/4...Nf6/5. Nc3/5...e5/6. Ndb5/6...d6/7. Bg5/7...a6

The primary purpose of 7...a6 is to drive the knight on b5 away from its strong position. The knight on b5 threatens to jump to c7, which would be a fork on Black's king and rook, and puts pressure on d6. By pushing the a-pawn, Black gains space on the queenside, which can support further pawn advances like ...b5, potentially leading to active counterplay on that side of the board. Forcing the knight to retreat diminishes White's immediate threats and allows Black to better organize their pieces. The knight typically moves to a3, where it is less active compared to b5.