Quick answer
Cross-Pin is a tactical idea: a line piece pinned to the king. Work from the first evidence position for Cross-Pin, and begin by testing Kf8.
Begin from Kf8 in 4k3/3n4/B7/8/8/8/8/4K3 b - - 1 1. Start with the forcing geometry: checks, captures, threats, defenders and flight squares around the target. The evidence answer is: Cross-Pin: check whether the pinned defender can legally move and what happens after the capture. Candidate line: Kf8.
In the Cross-Pin example, notice: side Black; pieces Black king e8, Black knight d7, White bishop a6, White king e1; legal first moves Kf8, Kf7, Ke7, Kd8, Nb8, Nf8, Nf6, Ne5. The candidates above are taken from this FEN snapshot and should be re-checked on any new board.
The tactical trigger
The first evidence board tests a line piece pinned to the king; the second board tests a line piece pinned to the king. Use direct FEN setup to reconstruct A and direct FEN setup to reconstruct B when the evidence includes move text. Shared language is catalogued on the Chess Wiki and the Tactics hub. Then compare Candidate Moves with Relative Pin, X Ray Attack, X Ray Defense around the final simplification.
The two inventories make the distinction concrete. A contains side Black; pieces Black king e8, Black knight d7, White bishop a6, White king e1; legal first moves Kf8, Kf7, Ke7, Kd8, Nb8, Nf8, Nf6, Ne5; B contains side Black; pieces Black king d8, Black knight f8, White bishop b5, White king g2; legal first moves Ke7, Kc7, Kc8, Nh7, Ng6, Ne6, Nd7. Compare the side to move before comparing the labels in the context of the last safe flight square.
Topic dossier for this page and board pair r1:4k3 | r2:3n4 | r3:B7 | r4:8 | r5:8 | r6:8 | r7:8 | r8:4K3 / r1:3k1n2 | r2:8 | r3:8 | r4:1B6 | r5:8 | r6:8 | r7:6K1 | r8:8: start with the final simplification; then test the last safe flight square; keep the overloaded attacker separate from the only defensive interposition; use the mating net's boundary as the transfer check; and reserve the exchange that removes a guard for the exception.
Calculation order
On the first board, calculate Kf8 after Kf8 and write down the opponent's best reply around the final simplification. On the second board, calculate Ke7 after Ke7 and check the last safe flight square. Calculate the most forcing move first, then test the opponent's best capture, interposition or counter-check before naming the motif. In this case the useful condition is the exchange that removes a guard.
Key claim: Cross-Pin is illustrated here by a line piece pinned to the king; the first concrete test is Kf8. The board anchor is 4k3/3n4/B7/8/8/8/8/4K3; the example is intentionally narrower than the topic label and should not be generalised without checking the surrounding position..
Practical boundary: To answer “How can a player recognize cross-pin, calculate the winning idea, and test the defender's best resource?”, compare the recorded setup with Ke7 and the opponent's reply. The decision is useful only when the stated condition survives that concrete test on board 3k1n2/8/8/1B6/8/8/6K1/8. The evidence records Illustrative evidence for the stated mechanism; it is not a claim that the candidate move is forced or best in every position and the second board signature r1:3k1n2 | r2:8 | r3:8 | r4:1B6 | r5:8 | r6:8 | r7:6K1 | r8:8. The false-positive test is whether the overloaded attacker appears without the only defensive interposition, so the conclusion is useful only when the stated condition survives that concrete test.
Evidence positions
example-1: a line piece pinned to the king
Show answer
Cross-Pin: check whether the pinned defender can legally move and what happens after the capture. Candidate line: Kf8.
Why this position is here: Cross-Pin is represented by a line piece pinned to the king. This is a direct FEN setup with board anchor 4k3/3n4/B7/8/8/8/8/4K3; no opening history is inferred from the diagram.
FEN: 4k3/3n4/B7/8/8/8/8/4K3 b - - 1 1
Question: What is the first concrete decision in this cross-pin position?
Answer cue: Cross-Pin: check whether the pinned defender can legally move and what happens after the capture. Candidate line: Kf8. The first candidate to test is Kf8. Replay Kf8 on board anchor 4k3/3n4/B7/8/8/8/8/4K3 and write down what changes after it.
Evidence boundary: Illustrative evidence for the stated mechanism; it is not a claim that the candidate move is forced or best in every position.
example-2: a line piece pinned to the king
Show answer
Cross-Pin: check whether the pinned defender can legally move and what happens after the capture. Candidate line: Ke7.
Why this position is here: Cross-Pin is represented by a line piece pinned to the king. This is a direct FEN setup with board anchor 3k1n2/8/8/1B6/8/8/6K1/8; no opening history is inferred from the diagram.
FEN: 3k1n2/8/8/1B6/8/8/6K1/8 b - - 5 3
Question: What is the first concrete decision in this cross-pin position?
Answer cue: Cross-Pin: check whether the pinned defender can legally move and what happens after the capture. Candidate line: Ke7. The first candidate to test is Ke7. Replay Ke7 on board anchor 3k1n2/8/8/1B6/8/8/6K1/8 and write down what changes after it.
Evidence boundary: Illustrative evidence for the stated mechanism; it is not a claim that the candidate move is forced or best in every position.
example-3: a line piece pinned to the king
Show answer
Cross-Pin: check whether the pinned defender can legally move and what happens after the capture. Candidate line: Nd7.
Why this position is here: Cross-Pin is represented by a line piece pinned to the king. This is a direct FEN setup with board anchor 1n3k2/8/8/1B6/8/8/8/7K; no opening history is inferred from the diagram.
FEN: 1n3k2/8/8/1B6/8/8/8/7K b - - 5 3
Question: What is the first concrete decision in this cross-pin position?
Answer cue: Cross-Pin: check whether the pinned defender can legally move and what happens after the capture. Candidate line: Nd7. The first candidate to test is Nd7. Replay Nd7 on board anchor 1n3k2/8/8/1B6/8/8/8/7K and write down what changes after it.
Evidence boundary: Illustrative evidence for the stated mechanism; it is not a claim that the candidate move is forced or best in every position.
Reading the line
Read the first example (id example-1) as a complete record: continuation Kf8, source fide-laws. This is a direct FEN setup with board anchor 4k3/3n4/B7/8/8/8/8/4K3; no opening history is inferred from the diagram. If A does not expose a line piece pinned to the king, correct the evidence before relying on the prose.
Read the second example (id example-2) separately: continuation Ke7, source fide-laws. Its feature is a line piece pinned to the king; inventory side Black; pieces Black king d8, Black knight f8, White bishop b5, White king g2; legal first moves Ke7, Kc7, Kc8, Nh7, Ng6, Ne6, Nd7. Compare what changes between Kf8 and Ke7.
The defensive resource
The main mistake to avoid with Cross-Pin is spotting a familiar motif but failing to test the defender's strongest legal resource. In A, the missing condition must be located in r1:4k3 | r2:3n4 | r3:B7 | r4:8 | r5:8 | r6:8 | r7:8 | r8:4K3 after Kf8; in B, test it against r1:3k1n2 | r2:8 | r3:8 | r4:1B6 | r5:8 | r6:8 | r7:6K1 | r8:8 after Ke7.
For Cross-Pin, the first board's evidence boundary (after Kf8) is Illustrative evidence for the stated mechanism; it is not a claim that the candidate move is forced or best in every position. The second board's evidence boundary for Cross-Pin is Illustrative evidence for the stated mechanism; it is not a claim that the candidate move is forced or best in every position. If a trusted source or careful calculation changes the conclusion around the mating net's boundary, update both the evidence record and this article.
Practice from a real game
cover the answer, list checks and captures, and record the defender or escape square that decides whether the idea works. Start with A's side to move and r1:4k3 | r2:3n4 | r3:B7 | r4:8 | r5:8 | r6:8 | r7:8 | r8:4K3; record two candidates, the reply to Kf8 and the correction. Repeat with B's side to move and r1:3k1n2 | r2:8 | r3:8 | r4:1B6 | r5:8 | r6:8 | r7:6K1 | r8:8; the changed board tests transfer rather than diagram memory.
After the drill, compare your notes with Relative Pin, X Ray Attack, X Ray Defense through the only defensive interposition. Keep A's rejected alternative beside B's chosen line Ke7; this shows whether the conclusion survived a new board signature.
Sources and scope
Sources for Cross-Pin: 1chess.online editorial scope, FIDE Laws of Chess. Source ids are original-analysis, fide-laws. Primary evidence hook: fide-laws. Comparisons and practice notes are editorial. Evidence revision: 2026-08-remediation-r2.
Scope note for board pair r1:4k3 | r2:3n4 | r3:B7 | r4:8 | r5:8 | r6:8 | r7:8 | r8:4K3 / r1:3k1n2 | r2:8 | r3:8 | r4:1B6 | r5:8 | r6:8 | r7:6K1 | r8:8: this page does not claim that Kf8 is an engine principal variation, that an exact endgame result is verified when the evidence says it is not, or that a tool output replaces human calculation. The conclusion is limited to the recorded boundary and the exception the overloaded attacker.