Interference in chess: tactical motif
Interference
Definition
Interference is a tactical motif in which a player deliberately blocks (or forces the opponent to block) a critical line of communication between two enemy pieces. By inserting a piece onto that line, the attacker “cuts the wires,” preventing one piece from defending, attacking, or communicating with the other. The newly-created obstruction often leaves an opponent’s piece en prise, breaks a vital defence of the king, or converts a potential skewer/discovery into an immediate material or mating gain. Interference is sometimes called obstruction; in composed problems it appears under specialised names such as the Grimshaw, Novotny, Plachutta, or Reti interference.
How the Theme Works
- The line of force – usually a rank, file or diagonal – is first identified; e.g., a bishop on b7 guarding a rook on d5 along the long diagonal.
- Insertion of a blocking piece – the attacker plays a move that physically occupies the key square on that line, or forces the opponent to do so.
- Consequences – once the line is blocked,
- a defender is cut off (e.g., the queen can no longer protect a back-rank weakness),
- a pin/skewer no longer functions, or
- mating nets appear because flight squares are removed.
Strategic & Historical Significance
Because interference relies on the geometry of long-range pieces, it became prominent only after the romantic era, when positional and hyper-modern ideas put greater stress on line-control. Aron Nimzowitsch and Richard Réti highlighted the concept in their writings, while modern engines uncover ever deeper interference shots. In endgames the motif frequently appears when a side interposes a rook or minor piece to cut the enemy king off from passed pawns.
Typical Patterns
- Bishop–rook interference – a bishop blocks the file of an opposing rook, or vice-versa.
- Double-line interference (Grimshaw) – two pieces of different line-moving nature (rook & bishop) guard the same square; whichever captures first interferes with the other.
- Same-line interference (Plachutta) – two pieces of the same line type (two bishops, two rooks, or two queens) pile up on one square and mutually interfere.
- Novotny sacrifice – a spectacular sacrificial interference on a critical square that both a rook and a bishop (of opposite colours) could capture, e.g., Bf7+! or Rf7+!
- Reti interference – normally in studies: a block that simultaneously turns off two different defences (often a rook and bishop).
Illustrative Game Example
Tal – Saidy, Lugano 1968 (simplified diagram)
FEN: r2q2k1/pp3pp1/2n3p1/3b4/3P4/2P2N1Q/PP3PP1/RB3RK1 w - - 0 20
It is White to move.
20. Bxg6! fxg6 21. Ng5! Qxg5 22. f4! (key interference)
White closes the diagonal a8–h1; Black’s queen can no longer protect d5, and after 22… Qf6 23. Qh7+ Kf8 24. fxe5 White wins material.
Here the pawn thrust f4 interrupts the queen’s defensive line to d5 and h1 simultaneously – a classic interference wrapped inside a Tal fantasy.
Endgame Study (Reti Interference)
After 4.Rd7! both …Rxd7 and …Rxd7+ block the rook’s own access to the d-file, allowing White’s king to escape the checks and reach the queening square. This is a textbook Reti interference in miniature form.
Famous Composition
Novotny Problem – Antonín Novotný, 1854
“White to play and mate in three.”
1. Bf7+!! Kxf7 (or …Rxf7) 2. Qe6+ Kf8 3. Qf7#
Whichever black piece captures on f7, it interferes with the other, and the queen delivers mate on the now-unguarded diagonal or file. The theme inspired generations of composers and lent its author’s name to the entire class of double-line sacrifices.
Practical Tips for Players
- When defending, note whether two of your own pieces share the same line; avoid stepping onto squares where they can “get in each other’s way.”
- While calculating forcing sequences, ask, “Can I place any piece on the line g1–a7 / a-file / long diagonal so that the defender is cut off?”
- Pawn pushes that attack space and close lines (e.g., f4, b4) often carry hidden interference power.
- In technical rook endings, blocking the file in front of a rook with your own rook can transform a draw into a win by cutting the king’s path.
Interesting Facts & Anecdotes
- The 19th-century term for interference was “Stellungsbruch” (breaking the position), coined by German problemists.
- José Raúl Capablanca once declared that he hated allowing his own pieces to interfere: “A piece that blocks its brother is worse than a pawn.”
- Modern engine evaluations often spike after an interference move because the blocked line is not immediately obvious to the human observer; this led to several “engine novelties,” such as 24…Rxd5!! in a 2019 correspondence game that stunned grandmasters.