I was wondering about refs earlier. Clearly they can’t ref their own nations which in itself can be an issue, as the strongest nations generally have the best leagues and consequently have the best refs, and hence the best refs are often sent home as their nations go further in the tournament. England being a notable exception in recent years!!
But what about non-home nation, but clearly close relatives. Like the english refs covering an Irish / N.Irish game? And then further, with leagues being so cosmopolitan now, particularly the Premier league…. Clattenburg’s reffing a Belgian team where he has far more familiarity with the Belgian side due to most of them playing in England (Italy’s a relative exception as many Italian’s remain in Serie A)