Chess Opening Theory/1. e4/1...c6/2. d4/2...d5/3. Nc3/3...dxe4/4. Nxe4/4...Bf5/5. Ng3/5...Bg6/6. h4/6...h5

= 6. ...h5 =

Instead of the more traditional ...h6, here black opts to block the white pawn from advancing altogether. This is a rare move at the professional level, although not an inherently bad one (although castling kingside becomes more dangerous compared to ...h6 lines). White has a large variety of moves to play; 7. Nf3 develops a piece while 7. Nh3!?, aiming for an eventual Nf4, has also been attempted.

Theory table
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1.e4 c6 2.d4 d5 3.Nc3 dxe4 4. Nxe4 Bf5 5. Ng3 Bg6 6. h4 h5