Answers.Body: <p>OK, so this question is for chess problemists, especially fairy problemists.</p>
  <p>First, why does the exact classification of castling horizontal check matter? Clearly it matters whether a move is check or not, but that's easy to determine. But the flavour of the check is not so easy, and usually not so important.</p>
  <p>It's a bit like a soccer goal. It's very important we know whether a goal has been scored. But beyond that we might ask about the <em>manner</em> of the goal: was it a penalty kick, a header, an own goal or what? The manner is obvious 99% of the time, but in the 1% there are scrums of elbows and boots where it's hard to say exactly what happened.</p>
  <p>Unless there is a fairy condition or tourney theme which is sensitive to discovery, I would say that it's up to you to classify. In the case of a tourney, of course you can consult the tourney director.</p>
  <p>In the special case of rookhoppers replacing the rooks, I'm curious as to how castling is defined. Clearly one can have a rookhopper move Ra1-f1 or Rh1-d1, but that's not castling as the king remains stuck in the middle of the back rank. However it's defined, I still think it will be up to you to classify.</p>
  <p>And of course separate from castling, triple checks are easily possible when you have hoppers on the board!</p>
  
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Body: <p>As far as I know, there could be as many as four possible types of check if we want to be as specific as possible:</p>
  <p><strong>1)</strong> a simple &quot;active&quot; check. I am not sure if there is a separate term for this, so let me call it simple active. So, a simple active check arises when the piece that moves gives check by itself but does not open any lines of attack from any other friend piece.</p>
  <p><strong>2)</strong> a discovered check. It arises when recently moved piece does NOT give check by itself but opens exactly one line of attack. A rider-type piece (being either a queen, a rook or a bishop) was hidden behind the piece that just moved.</p>
  <p><strong>3)</strong> a common double check where we combine #1 and #2: we have a piece that moved. It gave a check by itself. Also, it opened <strong>exactly one</strong> line of attack of a distinct frienly piece.</p>
  <p><strong>4)</strong> a very rare type of double check when the just-moved piece did NOT give check by itself. However, it opened TWO straight lines of attack, each one by a different piece but of the same type! I am pretty sure this is only possible during en passant. Also, both checking pieces must be queens of same color. One line of attack on enemy king must be a file and another, a diagonal.</p>
  <p>However, there is one quite important complication. I have recently realized that a check in chess could arise from <strong>castling</strong>.</p>
  <p>I analyzed all list items again, and it seems that this last case does not fall under any of #1, #2, #3 or #4.</p>
  <p>So I am confused. The better you know chess rules, the more you get confused.</p>
  <p><strong>If a check arose from castling, would it be a discovered check (see # 2), or is it a totally distinct type of check?</strong></p>
  <p>Essentially, I want to add that the rook in this case is a very specific chess piece type — a hopper.
  <a href="https://en.wikipedia.org/wiki/Fairy_chess_piece#Hoppers" rel="noreferrer">https://en.wikipedia.org/wiki/Fairy_chess_piece#Hoppers</a></p>
  
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Comments.Text: A Type 4 check doesn't need two queens -- a rook and a bishop are enough. E.g. White: king on d3, pawn on e2; Black: rook on d5, bishop on e6, pawn on d4. Black gives check with the bishop on f5; White blocks with e2e4; and White gives a double check with d4xe3ep.
Comments.UserDisplayName: TonyK
Tags: <castling><check><unorthodox-pieces><discovered-check>
Title: A check given by castling: is it a discovered check or a special case?
ThreadText: # A check given by castling: is it a discovered check or a special case?
  
  (Asked by: username_0 on 2024-07-05)
  
  As far as I know, there could be as many as four possible types of check if we want to be as specific as possible:
  
  **1)** a simple "active" check. I am not sure if there is a separate term for this, so let me call it simple active. So, a simple active check arises when the piece that moves gives check by itself but does not open any lines of attack from any other friend piece.
  
  **2)** a discovered check. It arises when recently moved piece does NOT give check by itself but opens exactly one line of attack. A rider-type piece (being either a queen, a rook or a bishop) was hidden behind the piece that just moved.
  
  **3)** a common double check where we combine #1 and #2: we have a piece that moved. It gave a check by itself. Also, it opened **exactly one** line of attack of a distinct frienly piece.
  
  **4)** a very rare type of double check when the just-moved piece did NOT give check by itself. However, it opened TWO straight lines of attack, each one by a different piece but of the same type! I am pretty sure this is only possible during en passant. Also, both checking pieces must be queens of same color. One line of attack on enemy king must be a file and another, a diagonal.
  
  However, there is one quite important complication. I have recently realized that a check in chess could arise from **castling**.
  
  I analyzed all list items again, and it seems that this last case does not fall under any of #1, #2, #3 or #4.
  
  So I am confused. The better you know chess rules, the more you get confused.
  
  **If a check arose from castling, would it be a discovered check (see # 2), or is it a totally distinct type of check?**
  
  Essentially, I want to add that the rook in this case is a very specific chess piece type — a hopper.
  <https://en.wikipedia.org/wiki/Fairy_chess_piece#Hoppers>
  
  **Tags:** castling, check, unorthodox-pieces, discovered-check
  
  > **Comments:**
  > **username_1**: A Type 4 check doesn't need two queens -- a rook and a bishop are enough. E.g. White: king on d3, pawn on e2; Black: rook on d5, bishop on e6, pawn on d4. Black gives check with the bishop on f5; White blocks with e2e4; and White gives a double check with d4xe3ep.  
  
  ---
  
  ## 1 answers
  
  ### Answer by username_2 on 2024-07-05. Score: 9 | Accepted answer
  
  OK, so this question is for chess problemists, especially fairy problemists.
  
  First, why does the exact classification of castling horizontal check matter? Clearly it matters whether a move is check or not, but that's easy to determine. But the flavour of the check is not so easy, and usually not so important.
  
  It's a bit like a soccer goal. It's very important we know whether a goal has been scored. But beyond that we might ask about the *manner* of the goal: was it a penalty kick, a header, an own goal or what? The manner is obvious 99% of the time, but in the 1% there are scrums of elbows and boots where it's hard to say exactly what happened.
  
  Unless there is a fairy condition or tourney theme which is sensitive to discovery, I would say that it's up to you to classify. In the case of a tourney, of course you can consult the tourney director.
  
  In the special case of rookhoppers replacing the rooks, I'm curious as to how castling is defined. Clearly one can have a rookhopper move Ra1-f1 or Rh1-d1, but that's not castling as the king remains stuck in the middle of the back rank. However it's defined, I still think it will be up to you to classify.
  
  And of course separate from castling, triple checks are easily possible when you have hoppers on the board!
  
  
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