the.com/offside trap

means A defensive tactic in soccer where defenders step forward together just before the ball is played, deliberately leaving an attacker in an offside position.

from Not a word with ancient roots but a tactical term — 'offside' itself comes from sports' broader use of 'side' for team, combined with being on the wrong side of the last defender, a concept formalized in football's laws in the 1800s. 'Trap' is the plain English word for a snare, borrowed into football slang once coaches realized the offside rule could be weaponized rather than just obeyed. The phrase itself is 20th-century football jargon, coined once tacticians noticed that the rule rewarded choreography as much as defending.