Chess Opening Theory/1. e4/1...e5/2. Nf3/2...Nc6/3. Bb5/3...a6/4. Ba4/4...Nf6/5. O-O/5...Be7/6. Re1/6...b5/7. Bb3/7...O-O

Closed Ruy Lopez, 7...O-O
White's natural move in this position is
 * 8.c3, continuing with the plan of eventually playing d4. This invites the Marshall Gambit ...d5 in response, which White may or may not be happy about.

Or White can try to do without the move c3, taking advantage of the fact that Black's c6-knight can't currently come to a5 and swap the bishop off because the e5-pawn would fall.

With the move
 * 8. h3, White eyes a transposition back to the main line with 8...d6 9.c3, while reserving the option of reacting to ...d5 by quickly developing the b1-knight to c3, hence the name Ambidextrous Variation.


 * 8. a4 is a radical change of course and was Gary Kasparov's choice. White takes advantage of the fact that Black a) hasn't forced the move c3, and b) can't play ...c6 because the knight is needed on c6 to defend e5, and hatches a plan of ganging up on the adventurous Black b-pawn with a4 and Nc3, while incidentally giving the bishop a retreat square on a2.