When an immediate goalscoring opportunity is likely to occur and there is a tight, marginal offside call, the assistant referee should keep their flag down until the passage of play is completed.
Once the goalscoring opportunity is complete - either a goal is scored or the chance is gone - the assistant will then flag to indicate the initial offence. If a goal is scored the VAR will then review the offside judgement.
Where there is a clear and obvious goalscoring opportunity and the assistant referee is certain the attacker actively involved is in an offside position, then the assistant should indicate the offence immediately.
In both of these situations the referee should wait to blow the whistle until the immediate phase of play has ended.
Factual offside decisions will be based on the evidence provided by fully calibrated offside lines.
See also: How offsides are determined by VAR
Premier League's VAR principles
Clear and obvious
Referee Review Area (RRA)
Attacking possession phase
How offsides are determined by VAR
History of VAR
Frequently Asked Questions