Not really news to anyone, but still interesting...

Human eye "cannot spot offside"

This means the referee, or the referee's assistant, must be able to keep two players of the attacking team, two players of the defending team and the ball in their visual field in order to make a fully informed offside decision, Dr Maruenda argues.

Slight flaw in his reasoning there (in terms of the practical application of the offside law, anyway), as referees' assistants are expected to listen for the contact with the ball and keep their eyes on the defensive line, thus eliminating two factors from the equation.