It is one of the professional game's most fundamental principles, but the offside law continues to cause controversy on a regular basis
It seems simple enough in theory, but few football rules cause more debate and controversy than the offside law.
It became a talking point again at the conclusion of the 2016-17 English season, with Chelsea unhappy with the way Alexis Sanchez gave Arsenal the lead in the FA Cup final.
On that occasion, Alexis scored by latching on to the ball in the penalty area despite the nearby presence of Aaron Ramsey, who was in an offside position.