Chess Opening Theory/1. e4/1...a6/2. d4/2...b5/3. Nf3/3...Bb7/4. Bd3

= St. George Defence = At that point, Black will usually play e6 and Nf6 in any order.

/4...Nf6/ adds up pressure and forces 5. Qe2 (5. e5 would free the bishop line of fire).

/4...e6/ builds Black pawn center and takes control of key squares.

Theory table
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'1.e4 a6 2.d4 b5 3.Nf3 Bb7 4.Bd3'