user8291: Playing a lot of blitz online, from time to time I meet quite strong players who regularly use very dubious lines that can have some shock or practical value in blitz or bullet chess, such as these, as White:
[FEN ""]

1.e4 e5 2.Bc4 Nf6 3.Bxf7+

Or, as Black:
[FEN ""]

1.e4 e5 2.Nf3 Bc5 3.Nxe5 Nc6


[FEN ""]

1.e4 e5 2.Nf3 d6 3.d4 Bg4 4.dxe5 d6


[FEN ""]

1.e4 d5 2.exd5 Qxd5 3.Nc3 Qe6+ with Qg6 and an early Nc6-b4 attack

I was wondering if all of this means that some players have their private analysis of some (objectively bad) lines for use in speed chess. 
Are you aware of other similar lines? As you can see, I don't mean Grob's Gambit or Cochrane's Gambit, but the very bad lines...

user14789: Yes, there are quite a few dubious lines one could try out when there is nothing much at stake.
1.d4 e5 2.dxe5 f6 comes to mind.
There was a book on blitz openings, but those variations are "fundamentally sound" according to the reviewer. 

user20776: A qualified yes.   I played in Philadelphia in the mid 50s and ran into a weird opening that is probably sound if not the best and had trouble with it. Turns out it was very popular in the Philly area but unheard of , back then, anywhere else. Now it is in opening books and even has a name. 

user7473: There are tons of first 4 moves that involve ridiculously unsound sacrifices, but most of these usually involve Bxf7+ and have no place in opening theory.
These 'openings' are largely based on a gross overvaluation of castling rights: you can just slowly castle by hand, especially since the attacker usually has no other pieces developed yet (e.g. after 1.e4 e5 2.Bc4 Nf6 3.Bxf7+ Kxf7, the only developed piece is black's); if the defender loses, it's a result of being outplayed, and is no fault of the opening.
Therefore, such lines are hardly worth studying to defend against, and even worse to learn to use. Just fall back to basic principles (develop your pieces, do not play h6 without thinking it through...) when facing these, and you will emerge with a long-term advantage.

user19861: Sometimes there's some practical value in taking a line others feel is unplayable and making it somewhat playable. At best, you should be aiming for a line that gives the opponent lots of chances to go wrong but allows you drawing chances if the opponent plays perfectly. I could give ideas but your opponent could be reading this too. It's best to come up with your own ideas. 
Some examples though: 
I recall Silman analyzing Damiano's defense and concluding that black's side was playable. 
I remember years ago playing a Fried Liver as white on FICS. My opponent was undoubtedly using an engine. I lost and lost badly but that just goes to show what you can do if you analyze deeply enough. 
I sometimes play the Englund gambit (1.d4, e5) as black. I can equalize about 99% of the time. 

user11629: In bullet chess (1 min or less), you basically don't have time for thinking and will pre-move or make moves instantaneously often making assumptions about your opponent's moves. In such situation playing the best moves becomes less important; basically you just need to move fast without blundering too much. Playing chess at such short times becomes more about bluffing and less about thinking.
The practical value of dubious lines/moves can be two-fold:

your opponent has to think (=losing valuable time) to refute the move
your opponent plays a standard (pre-move) which is not the best in this situation

Due to the limited time it is difficult to refute such dubious lines even if you lose a minor piece. So there is little risk involved.
I doubt there is much private analysis involved.  I also doubt there is much value in trying this at longer times (3 min or more).

8291: <p>Playing a lot of blitz online, from time to time I meet quite strong players who regularly use very dubious lines that can have some shock or practical value in blitz or bullet chess, such as these, as White:</p>

<pre><code>[FEN ""]

1.e4 e5 2.Bc4 Nf6 3.Bxf7+
</code></pre>

<p>Or, as Black:</p>

<pre><code>[FEN ""]

1.e4 e5 2.Nf3 Bc5 3.Nxe5 Nc6
</code></pre>

<hr>

<pre><code>[FEN ""]

1.e4 e5 2.Nf3 d6 3.d4 Bg4 4.dxe5 d6
</code></pre>

<hr>

<pre><code>[FEN ""]

1.e4 d5 2.exd5 Qxd5 3.Nc3 Qe6+ with Qg6 and an early Nc6-b4 attack
</code></pre>

<p>I was wondering if all of this means that some players have their private analysis of some (objectively bad) lines for use in speed chess. </p>

<p>Are you aware of other similar lines? As you can see, I don't mean Grob's Gambit or Cochrane's Gambit, but the very bad lines...</p>
 14789: <p>Yes, there are quite a few dubious lines one could try out when there is nothing much at stake.<br>
1.d4 e5 2.dxe5 f6 comes to mind.</p>

<p>There was a <a href="http://www.thechessmind.net/blog/2016/1/22/a-brief-review-of-the-sveshnikovs-a-chess-opening-repertoire.html" rel="nofollow noreferrer">book on blitz openings</a>, but those variations are "fundamentally sound" according to the reviewer. </p>
 20776: <p>A qualified yes.   I played in Philadelphia in the mid 50s and ran into a weird opening that is probably sound if not the best and had trouble with it. Turns out it was very popular in the Philly area but unheard of , back then, anywhere else. Now it is in opening books and even has a name. </p>
 7473: <p>There are tons of first 4 moves that involve ridiculously unsound sacrifices, but most of these usually involve Bxf7+ and have no place in opening theory.</p>

<p>These 'openings' are largely based on a gross overvaluation of castling rights: you can just slowly castle by hand, especially since the attacker usually has no other pieces developed yet (e.g. after 1.e4 e5 2.Bc4 Nf6 3.Bxf7+ Kxf7, the only developed piece is black's); if the defender loses, it's a result of being outplayed, and is no fault of the opening.</p>

<p>Therefore, such lines are hardly worth studying to defend against, and even worse to learn to use. Just fall back to basic principles (develop your pieces, do <em>not</em> play h6 without thinking it through...) when facing these, and you will emerge with a long-term advantage.</p>
 19861: <p>Sometimes there's some practical value in taking a line others feel is unplayable and making it somewhat playable. At best, you should be aiming for a line that gives the opponent lots of chances to go wrong but allows you drawing chances if the opponent plays perfectly. I could give ideas but your opponent could be reading this too. It's best to come up with your own ideas. </p>

<p>Some examples though: 
I recall Silman analyzing Damiano's defense and concluding that black's side was playable. </p>

<p>I remember years ago playing a Fried Liver as white on FICS. My opponent was undoubtedly using an engine. I lost and lost badly but that just goes to show what you can do if you analyze deeply enough. </p>

<p>I sometimes play the Englund gambit (1.d4, e5) as black. I can equalize about 99% of the time. </p>
 11629: <p>In bullet chess (1 min or less), you basically don't have time for thinking and will pre-move or make moves instantaneously often making assumptions about your opponent's moves. In such situation playing the best moves becomes less important; basically you just need to move fast without blundering too much. Playing chess at such short times becomes more about bluffing and less about thinking.</p>

<p>The practical value of dubious lines/moves can be two-fold:</p>

<ul>
<li>your opponent has to think (=losing valuable time) to refute the move</li>
<li>your opponent plays a standard (pre-move) which is not the best in this situation</li>
</ul>

<p>Due to the limited time it is difficult to refute such dubious lines even if you lose a minor piece. So there is little risk involved.</p>

<p>I doubt there is much private analysis involved.  I also doubt there is much value in trying this at longer times (3 min or more).</p>
