411 REFERENCE · Wikibooks
Chess Opening Theory/1. d4/1...Nf6/2. c4/2...g6/3. Nc3/3...d5/4. cxd5/4...Nxd5/5. e4/5...Nxc3/6. bxc3/6...Bg7/7. Nf3/7...c5/8. Bb5
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This check is an attempt to provoke concessions by Black who has three options now. Clearly the main move is 8...Nc6, which develops the knight on its best square but allows complications after 9.d5.
8...Bd7 9.Be2 leads to a slightly better position for White who profits from the fact that the pressure on d4 has been reduced for the moment.
8...Nd7 places the knight on a passive square. There will be no serious pressure against d4 now, and White should have the better chances thanks to his pawn centre.Grünfeld Defence rd nd bd qd kd rd pd pd pd pd bd pd pd bl pd pl pl pl nl pl pl pl pl rl bl ql kl rl
8.Bb5+
This check is fine since Black cannot block with ...c6, and thus should play Nd7. If Black wants a dull, equal position with no dynamic energy, he can play Bd7. Black is fine here.