411 REFERENCE · Wikibooks
Chess Opening Theory/1. e4/1...c5/2. d4/2...cxd4/3. c3/3...d3
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Smith-Morra Gambit Declined rd nd bd qd kd bd nd rd pd pd pd pd pd pd pd pl pl pd pl pl pl pl pl rl nl bl ql kl bl nl rl Sicilian Defence
3...d3
Players have played this move a bit, but it is too passive. Black does not need to decline White's gambit. After c4 followed by Bxd3, White has a Maróczy Bind and a spatial plus.
However, this move is very much playable, and even poses some specific benefits over 3...d5: specifically, it allows Dragon players to continue going for their fianchetto plans, and Najdorf/Kan/O'Kelly players to continue with their flexible ideas and setups, allowing lower-level players to still stick to their prep more or less.
Sicilian Defence, Smith–Morra Gambit