“Which-hunting” refers to editing which and that based on the superstition that the former should be used with a nonrestrictive clause and set off by commas; editors enslaved to this doctrine scrutinize manuscripts for relative clauses and zealously change whiches to thats or encase them in commas, with the satisfaction of someone lining up the pencils on their desk until they’re all perfectly parallel. This often produces esthetically displeasing results, but rarely does it have the potential of wreaking such havoc as in a sentence (Decision 4 of the International F.A. Board to Law 12 – Fouls and Misconduct) from soccer/football’s Laws of the Game:
A tackle, which endangers the safety of an opponent, must be sanctioned as serious foul play.
Since other versions (e.g., French: “Un tacle qui met en danger l’intégrité physique d’un adversaire doit être sanctionné comme faute grossière”) make it clear that the clause was meant to be restrictive, proper which-hunting would have turned the sentence into “A tackle that endangers…” But it’s so easy to get caught up in the game of changing whiches to thats that you lose sight of the point of it all and run the risk of this sort of thing. If I were a referee, I would zealously whistle every single tackle, explaining that Decision 4 of the IFAB banned tackles altogether and handing them a card with the phone number of whoever approved this abomination. Of course the Fédération Internationale de Football Association (FIFA) probably doesn’t recognize the English version of the rules as definitive, but it would be fun until I got a cease-and-desist call from Zurich or was stomped to death by outraged players, whichever came first. (Via Mark Liberman’s Language Log post.)
Note decisions 5 and 6 to the same Law, the former showing a similar application of the “rule” and the latter showing that who clauses escape the excrescent commas:
Any simulating action anywhere on the field, which is intended to deceive the referee, must be sanctioned as unsporting behaviour.
A player who removes his jersey when celebrating a goal must be cautioned for unsporting behaviour.