What's the most frequentlyl mis-played opening by amateurs?

Edit: fixed diagram. Also tried to make question more clear:

Which opening serves as the seeds of destruction in very specific ways more than any other opening at the amateur level?

My vote is for the French advance variation. In my own experience as a French player I now have around 30 OTB games in the French, 15 of them are the advance varation and 8 of those start with a position such as the following:

 Not all of these are games against low rated players either. Some of these are against 1700s!

What is it about the French that encourages white to go so badly wrong in such a predictable way? Let's be clear, Bb5 is a bad move in the French Advance! I did a search on Megabase 2012 for all games with white bishop on b5 with ECO C02.

1-0 - 492 Games = 24.8% Total 32.6%

1/2-1/2 - 308  Games = 15.5%

0-1 - 1184 = 5.7% Total 67.4%

What other commonly played openings are as badly mishandled regularly by amateur players?

from my (not so great) experience it is King's Gambit. I play it exclusively as White against 1.e4 e5 and against lower rated players (<1750) I have no problems to gain at least advantage, usually just small problems to win the game. Against stronger players it is something different, but your question was about "the lesser opponents" :)

Are they making specific opening mistakes or just making less than optimal moves frequently? My example, Bb5 in the French is really a huge mistep, arguably a blunder, going from a small statistical advantage for white to a huge statistical advantage for black. And it accounts for 1/2 of the games I've played in this variation. Do you see the same thing in the King's Gambit, where the lower rated players go wrong in very specific ways frequently, or is it just general less than optimal play at all phases?

If it's the latter that's more of an opening that's hard to play rather than an opening that is simply being played wrong in a very specific way, which isn't quite what I'm asking about, but is still useful to know.

Well, I think I can't answer your question exactly, because they are making mistakes of all kinds. For example 1.e4 e5 2.f4 exf4 3.Nf3 b6?? or something like 3..Qf6?, or sometimes in the process of the opening moves like a6 or c6.. There is not a specific move repeating itself like you mentioned, but to present an amateur with KGA is in my opinion perhaps the most difficult task you can give him. I tried quite few gambits (I bet some of them even didn't have a name) against 1.e4 e5 and I still like KG the most.

Looking again at the position you gave with White to move, isn't it wrong? Black moved 5 times, while White 6, for example 1.e4 e6 2.d4 d5 3.e5 c5 4.c3 Nc6 5.Nf3 Qb6 6.Bb5??? ?

1. e4 e6 2. d4 d5 3. e5 c5 4. Nf3 Nc6 5. c3 Qb6 6. Bb5
*

is the moves I entered. Not sure why it says "white to move" It should be black's move in that position, I'll see if I can figure out how to change that :)

You're saying half the people you have played OTB in the advance, played a move which looks to me like hanging the bishop?

Gah, here's why I should have the stupid sheet in front of me when I enter moves corrected position above. Doesn't change the search I did C02 with white Bb5 prior to move 8 as search criteria.

King's Gambit, Benko Gambit, Benoni, Cambridge Springs...At some point or other, amateurs misplay ALL openings.

Yes but are they misplayed in predictable specific ways with great frequency? I get that us class players make opening mistakes all the time. I'm not asking if we make opening mistakes. I'm asking, about openings which seem to be misplayed in very specific ways with great frequency. Which, I realize, is not at all clear from my first post.

Find out which openings are played most frequently by amateurs, and that provides your answer.  Q.E.D.

No, it doesn't.

I agree my question wasn't exactly clear.

Let me try to rephrase it:

The question is about specific repeated blunders by class players in the opening. As an example, in the French Advance (C02) the move Bb5 early is a huge, meaningful blunder, going from a position with relatively equal outcomes to a position with significant advantage for black. It's so bad as to be arguably a blunder. It is also a move that amateurs play frequently. In my own experience, more 1/2 of my French Advance games, 1/4 of all my French games, have this move at some point.

This suggests that amateurs misplay the French in a specific, predictable way. This is not merely making less than optimal moves in general, but making a specific bad move over and over again.

What other openings share this feature? Do any share it to the same degree as the French Advance?

Well as far as everything I've read goes the french is a difficult system especially for lower rated players. I'm a low rated player, <1400. I don't think I would have ever played Bb5 in french advance (which, if I see french I always prefer) unless I was playing a blitz game, in which the mistake is understandable.

Tell me that knight moved or am I imagining things?

alot people misplay QGD &QGA linescause there timeing for certain moves are usually off or they deviate early into worse moves.

alot people cant really play the Benoni to well either cause in that defense one must be willing to due some dynamic things or sufficate to death same goes for the KID & French Classical var.

In puttering around with 365chess.com's database for a bit, it looks to me like the largest number of games where white gets an overwhelming advantage because black has chosen an ultra-poor line follow from the variation beginning...

1.d4 d5 2.c4 Nf6. (or transposing from 1.d4 Nf6 2.c4 d5).

This scores around 70% for white, and occurred in ~5200 games from those two move orders.  If there's a higher number of bad results occurring for either player from a different move sequence, I was unable to find it.

For the most frequent unfortunate opening for white, I nominate...

1.e4 c5 2.Bc4...

Which scores something like 67% for black, and appeared in the database over 3000 times.

I think the King's Gambit (as black).

I've played it on quite a few occasions, but I still havn't gotten the hang of it!

Got to be at least in part because it's impossible.