Chess notation cheat-sheet (for new readers)
Pieces: K king · Q queen · R rook · B bishop · N knight · (a pawn move has no letter)
Actions: x takes · + check · # mate · O-O short castles · O-O-O long castles · e8=Q pawn promotes to queen
Annotations: ! good move · !! brilliant · ? mistake · ?? blunder
Cut the wire: positions where one defender guards two things at once
The setup that makes interference work is a single enemy piece stretched across two duties on one line. A rook on the back rank might guard mate on one square while it also covers a piece down the file. A bishop might hold a long diagonal that protects both a pawn and the escape route for its king. The defender is fine as long as that line stays open. Your job is to find a square on the line where you can drop a piece, breaking the connection so only one of the two jobs survives. These puzzles start you with clean two-target positions, then mix in cases where the second duty is hidden a move deeper. You learn to ask a plain question on every move: is an enemy piece doing double work along a rank, file, or diagonal? Once you spot that overload, the blocking square usually announces itself.
Reading which enemy line to block before you commit the piece
Find the guarding piece first. Before you toss a piece onto a square, name the defender and the exact line it works along. A rook guards a file; a bishop or queen guards a diagonal. Block the wrong line and you have just hung material.
Check the square is on the line of action. The interposing piece has to sit between the defender and its target, not merely near it. A square one rank off does nothing.
Confirm what survives the block. After the cut, the defender can still guard whatever sits on its other side. Make sure the thing you actually want, the mating square or the loose piece, is now stranded. I keep a short mental checklist on these, because it is easy to block a line and feel clever while the real target was never on it. Reading the board in that order, defender then line then target, turns a guess into a calculation.
Interference sacrifices that only work because the recapture is forced
Most interference in practice is a sacrifice. You plant a piece on the line knowing it can be taken, and the whole idea hinges on the recapture being forced or simply bad to decline. Two things make that happen. First, the object behind the cut is worth more than the piece you give up, so even an even trade leaves you ahead once the line stays blocked. Second, the interposing move carries its own threat, a check, a mate, or a fork, so the defender cannot ignore it and quietly hold the line. These puzzles drill the harder version: positions where the sacrifice looks like a blunder until you see that capturing reopens nothing useful, and declining loses on the spot. Positions in the trainer come from real games, computer-checked, which means every forced line you work through is one a real player faced rather than a setup arranged for a problem book.