The problem assistant referees face is they have to work to their normal system of officiating one week and then use VAR the next.
In Premier League matches without VAR they are asked to make judgement calls on tight offsides.
So when Erik Lamela was played through on goal at Stamford Bridge the linesman flagged for offside. It was very tight.
But when VAR is there, assistant referees need to keep their flags down when the offside is marginal so that play can continue and we see what happens.
If a goal is scored, for example, VAR will then go back and either support or correct the decision. That is the way VAR was used at the World Cup. It worked really well in Russia.
But if an assistant referee gets a marginal offside wrong, then they stop the outcome before it can happen and that defeats the object of VAR.
