How should one continue development against an unorthodox move by an opponent?

Question

Let's say you have been practicing a certain opening such as the Ruy Lopez and you have all the main lines down and suddenly your opponent makes some unorthodox move that you did not encounter while studying the Ruy Lopez, so you think to yourself, "Does my opponent have something up their sleeve?" or "My opponent does not know what they are doing". If you think the opponent has something up their sleeve like a trap, you might start to panic and blunder and make irrational moves yourself out of paranoia, but you might start to make irrational moves if you think your opponent doesn't know what they are doing when in fact they do.

So I guess the question boils down to this: How do you know when a move your opponent has made is a sound move (especially if you are a beginner) as opposed to a not so sound move? And once you have made the decision on whether the move was good or not, how do you proceed with development?

Answer 1

There are reasons why the main variations of an opening are "established," and why certain moves are seldom played. If a move is "unusual," there is probably something wrong with it.

So figure out why it is wrong. Maybe it gets the other player behind in development, or exposes a queen, or weakens a pawn. Once you have figured out what is wrong with the move, it is relatively easy to play against it.

Example: In the Ruy Lopez, you (White) and your opponent might play 1. e4 e5. 2. Nf3 Nc6. 3. Bb5 So far so good. But now Black plays 3... Nd4, a "strange" move that moves a knight twice in succession. It forks your N and B so the e pawn isn't really en prise. But now you play 4 NxN, and when Black recaptures on d4, he's got doubled d pawns, and has wasted a move. You can castle, 5. O-O, and have a significant lead in development.

Answer 2

How should one play against unexpected opening variations?

In short: calmly. In general, but especially in an opening you've prepared, the best defense against an unexpected move is to figure out the answers to two natural questions:

1. What is the purpose of this deviation? A threat? A trap? Perhaps your opponent wants to transpose into a line that's more comfortable for him, or less comfortable for you. Whatever the case, try to see what your opponent hopes to gain.
2. Why isn't this a common variation? Why didn't you come across it in your studies? Especially in the opening, if you encounter something unexpected, it's probably because it isn't as strong as the main lines. Try to see why: maybe it's an easily-refuted threat, or a loss of time, or it weakens your opponent's long-term position.

When you've answered these questions, if you've identified a credible threat, you must of course meet it. But if you can't determine an obvious threat posed by the unusual move, the best course is usually to relax and continue to make good, solid opening moves. Trust your fundamentals: they're guidelines that exist for a reason. Keep developing your pieces to good squares and watch for anything else unexpected. If you identified a weakness in your opponent's unusual move, take advantage of it where you can.

For example, given your opening of choice, a little-used variation of the Ruy Lopez:

[FEN "r1b1kbnr/ppppqppp/2n5/1B2p3/4P3/5N2/PPPP1PPP/RNBQK2R"]
1.e4 e5 2.Nf3 Nc6 3.Bb5 Qe7

Here, Black chooses a very unlikely third move. It doesn't pose any immediate threats (1), and it hinders his development by blocking in the King's Bishop (2). There's nothing White can do at the moment to take advantage of this strange choice directly, so he should continue with simple, easy development. 4.O-O leaves the BQ staring at nothing in particular. After the most common continuation, 4...Nd8 5.d4 c6 6.Ba4, White has done nothing special at all, but he's ahead in development while Black struggles to organize his troops.

[FEN "R1B1KBNR/PPPPQPP/2N5/1B2P3/4P3/5N2/PPPP1PPP/RNBQK2R"]
1.e4 e5 2.Nf3 Nc6 3.Bb5 Qe7 4.O-O Nd8 5.d4 c6 6.Ba4