This is an opening trap in what Brian Wall calls the "Nymphomaniac Attack" (1. e4 c6 2. Nf3 d5 3. e5!)
David Kane, creator of the coffeehouse chess video series has even created a Nymphomaniac Attack video.
http://www.youtube.com/watch?v=MaHKGIvTMFQ
This video is outstanding, and shows all kinds of cool tricks and traps in this
opening. I watched several of his videos and loved all of them. Very well organized, with a great sense of humor, and not taking himself (or the openings) too seriously.
As Brian's game below shows, even strong players (here an International Master!) can fall for these types of traps.
I have played similar traps and tactics in the Grob opening.
Here is the complete game:
[Event "ICC 3 0"]
[Site "Internet Chess Club"]
[Date "2014.01.12"]
[Round
"-"]
[White "BrianWall"]
[Black "IM : Ruslan Yandarbiev"]
[Result "1-0"]
[ICCResult "Black resigns"]
[WhiteElo "2080"]
[BlackElo "2034"]
[Opening "Caro-Kann defense"]
[ECO "B10"]
[NIC "CK.01"]
[Time "02:49:39"]
[TimeControl "180+0"]
1. e4 c6 2. Nf3 d5 3. e5 Bg4 4. d4 e6 5. c3 c5 6. dxc5 Bxc5 7. Qa4+
{Black resigns}
1-0
You can play through this game here: http://www.viewchess.com/cbreader/2014/1/18/Game203142224.html
Answer:
7.Qa4+! forks the Black King and Bishop on g4.
This is a great tactic pattern to know. The keys are:
* black has played e6, which prevents the bishop from doing a retreat to block the check.
* black has not played Nf6, which would protect the bishop,
* the fourth rank is clear.