Flag Technique – Offside
If an A.R. is not totally sure about an offside offence, the flag should not be raised (FIFA recommendation).
The flag is to be raised with the right hand (better line of vision), change to be made BEFORE the flag is raised
If the flag is not seen immediately by the referee, the A.R. must keep signalling until it has been recognised or the ball is clearly in control of the defending team.