Chess Opening Theory/1. e4/1...a6/2. d4/2...b5/3. Nf3/3...Bb7

= St. George Defence = The pawn is under attack. Nc3 is impossible, so the only good move is /4. Bd3/.

Theory table
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'1.e4 a6 2.d4 b5 3.Nf3 Bb7'