In his article today at ChessBase, “A New Marshall Gambit,” Lars Schandorff discusses the line 1.e4 e5 2.Nf3 Nc6 3.Bb5 a6 4.Ba4 Nf6 5,O-O Be7 6.Re1 b5 7.Bb3 d6 8.c3 O-O 9.h3 Na5 10.Bc2 d5!? which might be called the "Marshall Two-Step" or "Delayed Marshall Gambit." Schandorff writes: "For a traditional chess mind it doesn't make sense and probably some of the ancient masters would turn in their graves if they knew about it. They always played the normal 10...c5 with a typical Ruy Lopez game. But ...d5? Are you serious?" In the new age of chess realism, though, we must say, "If it works, it's good" and the games that Schandorff cites prove that Black is doing well.
I first saw the line in Charbonneau - Benjamin, USCL 2007, which I annotated as part of my coverage of the New Jersey Knockouts. Later I saw mention of it at the ever-popular Streatham & Brixton CC Blog under "My Favourite Moves V." Most players point to Kuznetsov - Gajewski, Czech Open 2007 (annotated by Tony Kosten) as the first example, but Carlsen - Adams, World Cup 2007 (annotated by Goran Urosevic -- also at Chessgames.com) must be the most significant. In any event, I'm sure it's not the last we have seen of it.