How do you defend against 馬後炮 (horse behind cannon)?
These answers restate the rules implemented by our open-source engine, which follows the WXF laws for movement, checkmate and both repetition rulings: a side that forces a repetition by perpetual check or perpetual chase loses rather than drawing. The chase half has not been validated against the official casebook. Where an answer refers to a specific position, that position lives on the linked reference page, where the build verifies it before publishing.
Direct answer
The best defence is prevention: deny the horse its landing point, block its leg on the way, and never leave your general on a line where an enemy cannon can stand behind a horse. Once the check has been given, the useful replies are to put a second piece on the line or capture the cannon. Capturing the horse with another piece usually fails, because your capturing piece simply becomes the cannon's new screen.
How the pattern works
In 馬後炮 the horse stands on the general's line, two points away, covering the general's sideways escape points. The cannon stands behind it on the same line and gives check using the horse as its screen. The general cannot step sideways, cannot step along the line, and cannot reach the horse. See what 馬後炮 is for the full picture.
Stopping it before it forms
- Cover the landing point. The horse needs one specific point in front of your general. If an advisor, elephant or other piece guards it, the horse cannot settle there.
- Block the leg. A horse travelling toward your palace needs its leg point empty for each jump. A piece standing there stops it.
- Keep the line crowded. The cannon needs exactly one piece between it and your general. If two of your pieces already stand on that line, the horse's arrival does not create a check.
- Keep an escape point. A general with a free point off the line is much harder to mate this way.
When the check has already been given
A cannon check is broken whenever the number of pieces between cannon and general stops being exactly one. So moving any piece onto the line, between the cannon and the horse or between the horse and your general, blocks the check. Capturing the cannon also works.
Capturing the horse with another piece is the tempting move that fails: the capturing piece lands on the horse's point and the cannon still has one screen, so the check remains and the move is illegal.
Related questions
Can the general capture the horse?
Not in the usual form: the horse stands two points away, and the general moves one point at a time.
Does it matter which side the cannon is on?
No. The pattern works along a file or a rank, so check both directions from your general.
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