user109: When I encounter the Sicilian as White, I often will play the Smith-Morra Gambit.  My opponent played 4...e5, but this does not appear to be a very popular move as there are only 2 games on www.chessgames.com that have it, one of them being here, which is apparently the first ever Smith-Morra Gambit recorded.  I didn't even see Wikipedia give it as an option, so I was curious to know why 4...e5 is not popular or in other words, what drawbacks does it have?
[FEN ""]
1. e4 c5 2. d4 cxd4 3. c3 dxc3 4. Nxc3 e5


user1712: To summarize and without going into detailed variations, white has an easy game after e5 and all pieces can have perfect positions. 

Bc4 with pressure on f7, Nf3 attacking the e5 pawn, and if black is not careful Ng5.
Bg5 and Nd5, pinning Nf6 in some variations.
Qb3 adding more pressure on f7 and b7.
After castling, doubling rooks on the d-file with pressure on the d-pawn or bringing the rooks to the c and d files with possible threats like Nb5.

Positionally and tactically white should be winning!

user70: I could not find any master games which included 4. ... e5.  Of the amateur games I found, the move produced the worst '%age win' result for Black of all moves listed. (Black's best response?  4. Nf6, being prepared to retreat it back to g8 if White pushes the e pawn.  How the Hypermodernists would grin.  These are all amateur games, remember... so you'll have to do your own analysis.)
I see almost 80 games that include 4. ... e5.  White's wins about 70% of the time which is huge. Black's win percentage just under 21%.  The only responses recorded for White are  5. Bc4 and 5. Nf3 with the former being marginally more successful.
Here are some sample games.
This one is Erich Hoffman v Walter Geissler from the 2005 EU-ch Seniors.  ECO B21.


[fen ""]
1. e4 c5 2. d4 cxd4 3. c3 dxc3 4. Nxc3 e5 5. Bc4 Nf6 6. Qb3 d5 7. exd5 Bd6 8.  Bg5 h6 9. Bh4 g5 10. Bg3 a6 11. h4 g4 12. h5 Nbd7 13. Bh4 Qc7 14. Bg3 Nb6 15.  Be2 Bd7 16. Rd1 Rg8 17. Bd3 Qc5 18. Bb1 Qa5 19. Kf1 Rb8 20. Nge2 Rg5 21. Bh4  Rxh5 22. Ng3 Rxh4 23. Rxh4 Nfxd5 24. Nge4 Bf8 25. Nxd5 Bb5+ 26. Kg1 Nxd5 27.  Qxd5 Be7 28. Rxh6 1-0


The first thing that strikes me is White's 9th move, a uncomfortable attack on two of Black's weakest squares, b7 and f7.  Now Black's backward d pawn is a liability as he can't easily block the a2-g8 diagonal.  Black is forced to give the pawn back.  That being said, I don't see White getting any real traction here.  If Black castled on move 10 instead of playing g5 he'd have had even chances.  The path he chooses instead leads to a back-rank weakness that ends the game.  Stockfish wasn't impressed with the entire adventure between Black's g pawn and h-file Rook, or White's Bishop and h pawn.  While both players miss some chances for improving their positions, Black's shattered King-side pawns remain.  The game is back and forth from moves 13 to 22; either player could have gained an advantage. However Black's 23. ... Nfxd5 is tragic and ends Black's chances to survive.  After that he comes apart.
This one is Ondrej Gabris v Ladislav Kasas from SVK-chT1W 0405. ECO B21.  Both are rated between FIDE(?) 2050 and 2100 so these players are similar in strength to USCF Masters.  I'll post it without any Stockfish analysis as I am out of time.


[fen ""]
1. e4 c5 2. d4 cxd4 3. c3 dxc3 4. Nxc3 e5 5. Bc4 Nf6 6. Qb3 d5 7. exd5 Bd6 8.  Bg5 h6 9. Bb5+ Nbd7 10. Bxf6 Qxf6 11. Nf3 O-O 12. Ne4 Qe7 13. O-O Nf6 14. Nxf6+  Qxf6 15. Nd2 Bf5 16. Bd3 b6 17. Rfe1 Bc5 18. Bxf5 Qxf5 19. Re2 Rad8 20. Rae1 e4  21. Nxe4 Rxd5 22. Nxc5 Rxc5 23. Qa3 Qd7 24. h3 Ra5 25. Qb3 Qd5 26. Qb4 Qc5 27.  Qxc5 Rxc5 28. f4 g6 29. Kf2 Kg7 30. Rd2 Rfc8 31. Re7 R8c7 32. Rxc7 Rxc7 33. Ke3  Kf6 34. g4 Ke6 35. Ke4 f5+ 36. Kf3 Rc4 37. Re2+ Kf6 38. Rd2 Ke6 39. Re2+ Kf6  40. Rd2 1/2-1/2



user1211: When I play the Smith-Morra gambit, I attempt to entice black into playing this move via 3. Nf3:
[fen ""]
1.e4 c5 2.d4 cxd4 3.Nf3 e5 4.c3 (4. Nxe5? Qa5+) *

After 3. Nf3, I haven't announced my intention to play the gambit since it could transpose into mainline Sicilian Defence (although, black's 4...Qa5+ might commit you to it; see my recent question here).
Black's move 3... e5 indeed protects black's d4 pawn, since if 4. Nxe5? Qa5+.  However, white now plays the gambit move 4. c3.
I think ...e5 gives white a better game than one of the usual variations.  The usual themes with backwards pawns on a half-open file apply: ganging up on black's d6 pawn and d5 hole; if the d6 pawn is pinned, the e5 pawn is also weak.  There's also opportunity to pile up black's f7 pawn, which is typically awkward to defend using a minor piece.  However, it's not really all that bad; it's somewhat similar to the Sveshnikov variation of the Sicilian defence.
Comments:

I personally like swapping off white's dark squared bishop for black's f6 knight, then placing one of white's knights at d5.  Sooner of later, black will need to swap off his light squared bishop to dislodge the knight, thereby giving opposite-coloured bishops, a particularly important imbalance.  If I can't find the right attack, I can still swap off into an opposite-coloured bishop endgame, which is likely an easy draw despite being a pawn down.
I find black's ...Bg4 to be a very annoying move, since it pins the f3 knight against the queen, and threatens ...Nd4.  This seems to be the main advantage of ...e5 over ...e6.  Keep an eye out for this move; in some cases, it can be a game-changer.  Sometimes it's helpful to take time to play h3 to prevent this move.


user-1: Simply stated, it's because of Black's backward d-pawn; see http://en.wikipedia.org/wiki/Backward_pawn -- as opposed to other lines of this Gambit it gives White a definite weakness to focus on well through the opening and possibly the middle-game and beyond.

109: <p>When I encounter the <code>Sicilian</code> as White, I often will play the <code>Smith-Morra Gambit</code>.  My opponent played <code>4...e5</code>, but this does not appear to be a very popular move as there are only 2 games on <a href="http://www.chessgames.com" rel="nofollow noreferrer">www.chessgames.com</a> that have it, one of them being <a href="http://www.chessgames.com/perl/chessgame?gid=1028842" rel="nofollow noreferrer">here</a>, which is apparently the first ever <code>Smith-Morra Gambit</code> recorded.  I didn't even see <a href="http://en.wikipedia.org/wiki/Sicilian_Defence,_Smith%E2%80%93Morra_Gambit" rel="nofollow noreferrer">Wikipedia</a> give it as an option, so I was curious to know why <code>4...e5</code> is not popular or in other words, what drawbacks does it have?</p>

<pre><code>[FEN ""]
1. e4 c5 2. d4 cxd4 3. c3 dxc3 4. Nxc3 e5
</code></pre>
 1712: <p>To summarize and without going into detailed variations, white has an easy game after e5 and all pieces can have perfect positions. </p>

<ul>
<li>Bc4 with pressure on f7, Nf3 attacking the e5 pawn, and if black is not careful Ng5.</li>
<li>Bg5 and Nd5, pinning Nf6 in some variations.</li>
<li>Qb3 adding more pressure on f7 and b7.</li>
<li>After castling, doubling rooks on the d-file with pressure on the d-pawn or bringing the rooks to the c and d files with possible threats like Nb5.</li>
</ul>

<p>Positionally and tactically white should be winning!</p>
 70: <p>I could not find any master games which included <code>4. ... e5</code>.  Of the amateur games I found, the move produced the worst '%age win' result for Black of all moves listed. (Black's best response?  <code>4. Nf6</code>, being prepared to retreat it back to <code>g8</code> if White pushes the e pawn.  How the Hypermodernists would grin.  These are all amateur games, remember... so you'll have to do your own analysis.)</p>

<p>I see almost 80 games that include <code>4. ... e5</code>.  White's wins about 70% of the time which is huge. Black's win percentage just under 21%.  The only responses recorded for White are  <code>5. Bc4</code> and <code>5. Nf3</code> with the former being marginally more successful.</p>

<p>Here are some sample games.</p>

<p>This one is Erich Hoffman v Walter Geissler from the 2005 EU-ch Seniors.  ECO B21.</p>

<pre>
<code>
[fen ""]
1. e4 c5 2. d4 cxd4 3. c3 dxc3 4. Nxc3 e5 5. Bc4 Nf6 6. Qb3 d5 7. exd5 Bd6 8.  Bg5 h6 9. Bh4 g5 10. Bg3 a6 11. h4 g4 12. h5 Nbd7 13. Bh4 Qc7 14. Bg3 Nb6 15.  Be2 Bd7 16. Rd1 Rg8 17. Bd3 Qc5 18. Bb1 Qa5 19. Kf1 Rb8 20. Nge2 Rg5 21. Bh4  Rxh5 22. Ng3 Rxh4 23. Rxh4 Nfxd5 24. Nge4 Bf8 25. Nxd5 Bb5+ 26. Kg1 Nxd5 27.  Qxd5 Be7 28. Rxh6 1-0
</code>
</pre>

<p>The first thing that strikes me is White's 9th move, a uncomfortable attack on two of Black's weakest squares, <code>b7</code> and <code>f7</code>.  Now Black's backward <code>d</code> pawn is a liability as he can't easily block the <code>a2-g8</code> diagonal.  Black is forced to give the pawn back.  That being said, I don't see White getting any real traction here.  If Black castled on move 10 instead of playing <code>g5</code> he'd have had even chances.  The path he chooses instead leads to a back-rank weakness that ends the game.  Stockfish wasn't impressed with the entire adventure between Black's <code>g</code> pawn and h-file Rook, or White's Bishop and <code>h</code> pawn.  While both players miss some chances for improving their positions, Black's shattered King-side pawns remain.  The game is back and forth from moves 13 to 22; either player could have gained an advantage. However Black's <code>23. ... Nfxd5</code> is tragic and ends Black's chances to survive.  After that he comes apart.</p>

<p>This one is Ondrej Gabris v Ladislav Kasas from SVK-chT1W 0405. ECO B21.  Both are rated between FIDE(?) 2050 and 2100 so these players are similar in strength to USCF Masters.  I'll post it without any Stockfish analysis as I am out of time.</p>

<pre>
<code>
[fen ""]
1. e4 c5 2. d4 cxd4 3. c3 dxc3 4. Nxc3 e5 5. Bc4 Nf6 6. Qb3 d5 7. exd5 Bd6 8.  Bg5 h6 9. Bb5+ Nbd7 10. Bxf6 Qxf6 11. Nf3 O-O 12. Ne4 Qe7 13. O-O Nf6 14. Nxf6+  Qxf6 15. Nd2 Bf5 16. Bd3 b6 17. Rfe1 Bc5 18. Bxf5 Qxf5 19. Re2 Rad8 20. Rae1 e4  21. Nxe4 Rxd5 22. Nxc5 Rxc5 23. Qa3 Qd7 24. h3 Ra5 25. Qb3 Qd5 26. Qb4 Qc5 27.  Qxc5 Rxc5 28. f4 g6 29. Kf2 Kg7 30. Rd2 Rfc8 31. Re7 R8c7 32. Rxc7 Rxc7 33. Ke3  Kf6 34. g4 Ke6 35. Ke4 f5+ 36. Kf3 Rc4 37. Re2+ Kf6 38. Rd2 Ke6 39. Re2+ Kf6  40. Rd2 1/2-1/2
</code>
</pre>
 1211: <p>When I play the Smith-Morra gambit, I attempt to entice black into playing this move via <code>3. Nf3</code>:</p>

<pre><code>[fen ""]
1.e4 c5 2.d4 cxd4 3.Nf3 e5 4.c3 (4. Nxe5? Qa5+) *
</code></pre>

<p>After <code>3. Nf3</code>, I haven't announced my intention to play the gambit since it could transpose into mainline Sicilian Defence (although, black's 4...Qa5+ might commit you to it; see my recent question <a href="https://chess.stackexchange.com/questions/2262/how-to-best-respond-to-an-early-black-qa5-in-the-smith-morra-gambit">here</a>).</p>

<p>Black's move <code>3... e5</code> indeed protects black's <code>d4</code> pawn, since if <code>4. Nxe5? Qa5+</code>.  However, white now plays the gambit move <code>4. c3</code>.</p>

<p>I think <code>...e5</code> gives white a better game than one of the usual variations.  The usual themes with backwards pawns on a half-open file apply: ganging up on black's <code>d6</code> pawn and <code>d5</code> hole; if the <code>d6</code> pawn is pinned, the <code>e5</code> pawn is also weak.  There's also opportunity to pile up black's <code>f7</code> pawn, which is typically awkward to defend using a minor piece.  However, it's not really all that bad; it's somewhat similar to the <a href="http://en.wikipedia.org/wiki/Sicilian_Defence#Sveshnikov_Variation:_4...Nf6_5.Nc3_e5." rel="nofollow noreferrer">Sveshnikov variation of the Sicilian defence</a>.</p>

<p>Comments:</p>

<ul>
<li><p>I personally like swapping off white's dark squared bishop for black's <code>f6</code> knight, then placing one of white's knights at <code>d5</code>.  Sooner of later, black will need to swap off his light squared bishop to dislodge the knight, thereby giving opposite-coloured bishops, a particularly important imbalance.  If I can't find the right attack, I can still swap off into an opposite-coloured bishop endgame, which is likely an easy draw despite being a pawn down.</p></li>
<li><p><strong>I find black's <code>...Bg4</code> to be a very annoying move</strong>, since it pins the <code>f3</code> knight against the queen, and threatens <code>...Nd4</code>.  This seems to be the main advantage of <code>...e5</code> over <code>...e6</code>.  Keep an eye out for this move; in some cases, it can be a game-changer.  Sometimes it's helpful to take time to play <code>h3</code> to prevent this move.</p></li>
</ul>
 -1: <p>Simply stated, it's because of Black's backward d-pawn; see <a href="http://en.wikipedia.org/wiki/Backward_pawn">http://en.wikipedia.org/wiki/Backward_pawn</a> -- as opposed to other lines of this Gambit it gives White a definite weakness to focus on well through the opening and possibly the middle-game and beyond.</p>
