The Fishing Pole is a cheeky trap against the Ruy Lopez (and against an early castle in general). Black throws the knight forward to g4, lets White hook it, and the very capture that wins the knight tears open the h-file straight at White's castled king. It is named for the bait-and-yank pattern — the knight is the lure, the h-pawn is the line, and a greedy White is the fish.
After castling, Black plays …Ng4 and …h5, offering the knight; if White bites with hxg4, then …hxg4 opens the h-file and Black storms in with …Qh4 and …Qh1#.
The whole idea hinges on the half-open h-file. Black plays 4…Nf6 and, after 5.O-O, lunges with 5…Ng4, then 5…h5 to support it and to load the h-pawn. The knight looks like a free gift, but taking it is fatal: after 6.hxg4?? hxg4 the h-file is wide open with the rook on h8 bearing down on the king. White's 7.Nxe5 grabs a pawn but ignores the storm; 7…Qh4 brings the queen to the file with the deadly threat of …Qh1#, and after 8.Nxc6 (or any non-defence) 8…Qh1# delivers mate down the h-file, the king with no escape. If White simply refuses the bait, there is no trap at all.
6. hxg4 — After 5…h5 the losing move is 6.hxg4??, snapping off the 'hanging' knight. That capture is exactly what Black wants — it opens the h-file toward the king. Instead White should ignore the knight and play a calm move like 6.d3, 6.c3, or 6.Re1, when the g4-knight is just a misplaced piece Black has to retreat.
Never open a file toward your own king to win a stray piece. When a knight parks on g4 and the h-pawn comes up, treat the h-file as radioactive: don't play hxg4. Keep the file closed with a quiet developing move (d3, c3, Re1), let the over-extended knight stand there, and White ends up better with no risk at all.
Only if they grab the knight. A strong player ignores 5…Ng4, plays a quiet move like 6.d3 or 6.Re1, and Black's forward knight becomes a liability. The trap depends entirely on White opening the h-file with 6.hxg4.
Anything that leaves the h-file closed — 6.d3, 6.c3, or 6.Re1 are all comfortable. The g4-knight isn't actually doing anything, so there is no need to capture it and every reason not to.
A trap only works if your opponent makes the mistake — strong players sidestep these, which is why each page also shows how to avoid it. Every line here is checked legal with the same engine the board runs, and every checkmate is verified.