The pitchside screen

[ClaretTony]

The ball hadn’t gone out of play had it? He stopped the game with the ball still in play. I assumed on that basis they must have already checked the offside?

Just seen it back, we've just cleared the ball down the line and he blows with it just inside the Longside touchline around ten yards inside the Brentford half.

[MDWat]

All the more bizarre then but perhaps Claptrappers is right that they are advised to at an appropriate point with this instance being that nothing was happening.