[chaddeshon]

It's almost certainly playing out of an opening book.

There is a move history, but you have to expand it.

[asdfologist]

How does playing out of an opening book explain the opening blunder 2. e4?

[danielbarla]

Well, I guess if it really was out of a book, it would imply that the quality of the engine itself wasn't at fault, but rather a bad opening book. Also, without that line being thoroughly researched, it'd be difficult to say whether it's a blunder, or a clever sacrifice. Again, it could be an incomplete opening book which led the engine to offer the sacrifice, but then didn't have info on how to capitalise on it.

Though in this case, I think it's almost certainly a blunder, that line does not appear to be a well known opening.

[V-2]

There are opening books, and there are opening books. 1. Nf3 Nf6 2. e4 can no doubt be found in some opening books due to the sheer fact that someone, somewhere, played it, and it got archived. Then yes it's a line that could get selected at random.

It's not a serious opening though, it looks frivolous - could be played in simultaneous games, or in bullet chess for its surprise value etc.

If you optimize the opening book to include serious games only, you're unlikely to come across this line. http://www.chessgames.com/perl/explorer?node=98&move=2&moves...

Given the insame amount of opening theory research humanity has done by now, if e4 on the third move here was even remotely close to a clever sacrifice, chess community would have noted it by now.

[alextgordon]

Stockfish doesn't use an opening book, so unless MS added one to it, it is not.

[perlgeek]

I'd say the exact opposite is true. With an opening book, both would play a much stronger opening.

Without one, they have only a second to come up with an opening, so it's no surprise if the result is weird.