In an event I played in this past weekend, I was surprised when (playing Black) I encountered: 1. e4 e5 2. c3.
I'd never seen this opening before - later web searching told me that it is the Lopez Opening a/k/a MacLeod Attack (ECO code C20, which seems to cover several miscellaneous double king pawn openings). When I saw White's second move, I couldn't imagine what the purpose of it was, and was worried that I was missing some sort of obvious trap. But I didn't see one. The only thing I could think at the time was that my opponent was trying to get me "out of book", but at my level that's sort of pointless - I don't have much of a book to begin with... So I just fell back to general opening principles and played 2. ... Nf6. My opponent's continuation was the (possibly even more dubious) 3. d3. This all led to a fairly easy game for me, that I won in less than 20 moves.
Thinking about it afterwards, the most confusing thing was that this was played by a player with about 4 years of tournament experience rated about 150 points higher than me. So this wasn't someone who's just learning the game. So I'm just mystified as to why someone would play this opening. I tried to do some research to see if there are any lines that are good for White, but found that MCO and FCO don't even cover this opening. The opening explorer on 365Chess (which I admittedly don't know how big its database is, or where it gets its games) seems to indicate that the best continuations for Black are 2. ... Nf6 or 2. ... d5, with around a 75% winning percentage, or 2. ... Nc6, with more than an 80% winning percentage (but with a much smaller sample size than the other two).
Are there any reasonably rational plans for White with this opening that I haven't been able to find, other than just playing it for the "surprise factor"? Am I missing something obvious here?