Answers.Body: <p>One more scenario that has not been mentioned yet is that an unprotected interposing piece might unblock a sliding piece leading to a discovered check, which prevents the capture of the interposed piece, like in the example below:</p>
  
  <pre><code>[FEN "3r2k1/6pp/4R3/8/2R5/1B6/5PPP/r5K1 w - - 0 1"]
  
  1. Rc1 Rxc1+ 2. Re1+
  </code></pre>
  
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2021-03-25T04:02:59.913Z
Answers.Text: I guess you don't need a second white rook, to show this example.
Answers.UserDisplayName: eguneys
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2021-03-25T08:09:46.040Z
Answers.Text: The second rook exemplifies the point that the interposition can even be useful if it does not directly give check, but just enables a discovered check.
Answers.UserDisplayName: Fabian Fichter
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2019-08-04T10:03:53.160Z
Answers.LastActivityDate: 2019-08-04T10:03:53.160Z
Answers.UserDisplayName: Fabian Fichter
Answers.Body: <pre><code>[FEN "R5k1/5ppp/8/2r5/1b6/8/5PPP/6K1 b - - 0 1"]
  
  1... Rc8 2. Rxc8+ Bf8
  </code></pre>
  
  <p>This is an example of what Tim Krabbé calls an <a href="https://timkr.home.xs4all.nl/chess2/cql.htm" rel="noreferrer">'unguarded guard'</a> - a linepiece checks, and a piece interposes on an unguarded square. That page mentions Topalov - Polgar, Novgorod 1996 (see below); while not a true back rank mate, it comes close. <a href="http://www.arves.org/arves/index.php/en/endgamestudies/cql-sample-files/cql-unguarded-guard" rel="noreferrer">Here</a> are some endgame studies with other types of Unguarded Guards.</p>
  
  <pre><code>[FEN ""]
  [Event "Novgorod"]
  [Date "1996-07-27"]
  [White "Veselin Topalov"]
  [Black "Judit Polgar"]
  [StartPly "92"]
  
  1.e4 c5 2.Nf3 e6 3.d4 cxd4 4.Nxd4 Nc6 5.Nc3 Qc7 6.Be3 a6 7.Bd3
  b5 8.Nxc6 Qxc6 9.O-O Bb7 10.a3 Nf6 11.Re1 Be7 12.Qf3 d6 13.Qh3
  h5 14.Bg5 Qc5 15.Be3 Qc6 16.f3 g5 17.a4 b4 18.Na2 g4 19.fxg4
  d5 20.c3 bxc3 21.bxc3 Nxg4 22.Bd4 Bc5 23.Be2 Nf6 24.e5 Ne4
  25.Nb4 Bxd4+ 26.cxd4 Qb6 27.Nc2 Rc8 28.Rab1 Qa7 29.Bd3 Rg8
  30.a5 Bc6 31.Rb6 Bb5 32.Bxe4 dxe4 33.Rxe6+ Kf8 34.Qa3+ Kg7
  35.Re7 Rc7 36.Rxc7 Qxc7 37.Ne3 Kh8 38.Rc1 Qd8 39.d5 Qg5 40.Qc3
  Kh7 41.Qd4 Bd3 42.d6 h4 43.Rc7 Rb8 44.Rxf7+ Kg8 45.e6 Qxe3+
  46.Qxe3 Rb1+ 47.Qc1 Rxc1+ 48.Kf2 Rc6 49.Rd7 Bb5 50.Ke3 Rc2
  51.Rc7 Re2+ 52.Kf4 Rf2+ 53.Kxe4 Re2+ 54.Kf5 Rf2+ 55.Ke5 Re2+
  56.Kf6 Rf2+ 57.Ke7 Re2 58.d7 Bxd7 59.Kxd7 Rd2+ 60.Ke8 1-0
  </code></pre>
  
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2019-08-02T16:36:38.017Z
Answers.Text: I guess idea in this example is the only situation where this combination can be applied. Is there a name for this combination, eg. clearing the defender. Also a real example would be sweet.
Answers.UserDisplayName: eguneys
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2019-08-03T17:06:50.677Z
Answers.Text: @eguneys Is “clearance sacrifice” not specific enough?
Answers.UserDisplayName: 11684
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2019-08-03T20:22:52.700Z
Answers.Text: I'm totally not a chessplayer but I do know the rules. I'm curious - in move 47, why did white block with the queen? Couldn't he just do Kf2 right away?
Answers.UserDisplayName: Vilx-
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2019-08-03T20:30:18.597Z
Answers.Text: That would allow 47 ... Rf1 which is mate. White sacrifices a queen to let the king escape to e3.
Answers.UserDisplayName: Glorfindel
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2019-08-03T21:24:09.047Z
Answers.Text: Ah, yes, I see now. My untrained mind had skipped over the black pawns somehow. :)
Answers.UserDisplayName: Vilx-
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2019-08-02T16:13:20.797Z
Answers.LastActivityDate: 2019-08-02T16:47:10.133Z
Answers.LastEditDate: 2019-08-02T16:47:10.133Z
Answers.UserDisplayName: Glorfindel
Answers.Body: <p>A different, but similar, situation would be with a castled king, minus the rook, behind two pawns with a knight inbetween them.</p>
  
  <pre><code>[FEN "r3k3/8/8/8/8/8/5PNP/6K1 b - - 0 1"]
  
  1... Ra1+ 2. Ne1 Rxe1+ 3. Kg2
  </code></pre>
  
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2019-08-03T17:10:11.650Z
Answers.LastActivityDate: 2019-08-03T17:20:05.157Z
Answers.LastEditDate: 2019-08-03T17:20:05.157Z
Answers.UserDisplayName: 11684
Body: <p>Could the following situation possibly exist?</p>
  
  <p>It's White to play, and Black is about to get back rank mated. This is because the King's mobility is restricted to a single file. Then White gives a check.</p>
  
  <p>At this point, Black plays the best move that blocks with a hanging piece, where the blocking piece has no defense. White takes the piece with check, and black can now escape somehow. </p>
  
  <p>An example of this is that by blocking check with a hanging knight, Black opens up a bishop's path to further block, but this time safely and checkmate is avoided.</p>
  
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2019-08-02T19:24:47.327Z
Comments.Text: By "restricted to a single file" don't you mean "restricted to a single rank"? (Ranks go sideways, files go up and down.)
Comments.UserDisplayName: bof
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2019-08-02T19:28:20.597Z
Comments.Text: Is this an example of what you're talking about? Black has K on g8, N on g7, P on f7, g6, h7; White has R on a1, K on g1. Play goes 1.Ra8+ Ne8 2.Rxe8+ Kg7
Comments.UserDisplayName: bof
Tags: <tactics><checkmate>
Title: Can it be useful for a player block with a hanging piece in a back rank mate situation?
ThreadText: # Can it be useful for a player block with a hanging piece in a back rank mate situation?
  
  (Asked by: username_0 on 2019-08-02)
  
  Could the following situation possibly exist?
  
  It's White to play, and Black is about to get back rank mated. This is because the King's mobility is restricted to a single file. Then White gives a check.
  
  At this point, Black plays the best move that blocks with a hanging piece, where the blocking piece has no defense. White takes the piece with check, and black can now escape somehow.
  
  An example of this is that by blocking check with a hanging knight, Black opens up a bishop's path to further block, but this time safely and checkmate is avoided.
  
  **Tags:** tactics, checkmate
  
  > **Comments:**
  > **username_1**: By "restricted to a single file" don't you mean "restricted to a single rank"? (Ranks go sideways, files go up and down.)  
  > **username_1**: Is this an example of what you're talking about? Black has K on g8, N on g7, P on f7, g6, h7; White has R on a1, K on g1. Play goes 1.Ra8+ Ne8 2.Rxe8+ Kg7  
  
  ---
  
  ## 3 answers
  
  ### Answer by username_2 on 2019-08-04. Score: 4 | Accepted answer
  
  One more scenario that has not been mentioned yet is that an unprotected interposing piece might unblock a sliding piece leading to a discovered check, which prevents the capture of the interposed piece, like in the example below:
  
  ```
  [FEN "3r2k1/6pp/4R3/8/2R5/1B6/5PPP/r5K1 w - - 0 1"]
  
  1. Rc1 Rxc1+ 2. Re1+
  
  ```
  
  > **Comments:**
  > **username_0**: I guess you don't need a second white rook, to show this example.  
  > **username_2**: The second rook exemplifies the point that the interposition can even be useful if it does not directly give check, but just enables a discovered check.  
  
  ---
  
  ### Answer by username_3 on 2019-08-02. Score: 17
  
  ```
  [FEN "R5k1/5ppp/8/2r5/1b6/8/5PPP/6K1 b - - 0 1"]
  
  1... Rc8 2. Rxc8+ Bf8
  
  ```
  
  This is an example of what Tim Krabbé calls an ['unguarded guard'](https://timkr.home.xs4all.nl/chess2/cql.htm) - a linepiece checks, and a piece interposes on an unguarded square. That page mentions Topalov - Polgar, Novgorod 1996 (see below); while not a true back rank mate, it comes close. [Here](http://www.arves.org/arves/index.php/en/endgamestudies/cql-sample-files/cql-unguarded-guard) are some endgame studies with other types of Unguarded Guards.
  
  ```
  [FEN ""]
  [Event "Novgorod"]
  [Date "1996-07-27"]
  [White "Veselin Topalov"]
  [Black "Judit Polgar"]
  [StartPly "92"]
  
  1.e4 c5 2.Nf3 e6 3.d4 cxd4 4.Nxd4 Nc6 5.Nc3 Qc7 6.Be3 a6 7.Bd3
  b5 8.Nxc6 Qxc6 9.O-O Bb7 10.a3 Nf6 11.Re1 Be7 12.Qf3 d6 13.Qh3
  h5 14.Bg5 Qc5 15.Be3 Qc6 16.f3 g5 17.a4 b4 18.Na2 g4 19.fxg4
  d5 20.c3 bxc3 21.bxc3 Nxg4 22.Bd4 Bc5 23.Be2 Nf6 24.e5 Ne4
  25.Nb4 Bxd4+ 26.cxd4 Qb6 27.Nc2 Rc8 28.Rab1 Qa7 29.Bd3 Rg8
  30.a5 Bc6 31.Rb6 Bb5 32.Bxe4 dxe4 33.Rxe6+ Kf8 34.Qa3+ Kg7
  35.Re7 Rc7 36.Rxc7 Qxc7 37.Ne3 Kh8 38.Rc1 Qd8 39.d5 Qg5 40.Qc3
  Kh7 41.Qd4 Bd3 42.d6 h4 43.Rc7 Rb8 44.Rxf7+ Kg8 45.e6 Qxe3+
  46.Qxe3 Rb1+ 47.Qc1 Rxc1+ 48.Kf2 Rc6 49.Rd7 Bb5 50.Ke3 Rc2
  51.Rc7 Re2+ 52.Kf4 Rf2+ 53.Kxe4 Re2+ 54.Kf5 Rf2+ 55.Ke5 Re2+
  56.Kf6 Rf2+ 57.Ke7 Re2 58.d7 Bxd7 59.Kxd7 Rd2+ 60.Ke8 1-0
  
  ```
  
  > **Comments:**
  > **username_0**: I guess idea in this example is the only situation where this combination can be applied. Is there a name for this combination, eg. clearing the defender. Also a real example would be sweet.  
  > **username_4**: @username_0 Is “clearance sacrifice” not specific enough?  
  > **username_5**: I'm totally not a chessplayer but I do know the rules. I'm curious - in move 47, why did white block with the queen? Couldn't he just do Kf2 right away?  
  > **username_3**: That would allow 47 ... Rf1 which is mate. White sacrifices a queen to let the king escape to e3.  
  > **username_5**: Ah, yes, I see now. My untrained mind had skipped over the black pawns somehow. :)  
  
  ---
  
  ### Answer by username_4 on 2019-08-03. Score: 10
  
  A different, but similar, situation would be with a castled king, minus the rook, behind two pawns with a knight inbetween them.
  
  ```
  [FEN "r3k3/8/8/8/8/8/5PNP/6K1 b - - 0 1"]
  
  1... Ra1+ 2. Ne1 Rxe1+ 3. Kg2
  
  ```
  
  
  ---
  
  