the Eredivisie effect
The Eredivisie effect is caused by a football/soccer player leaving an easy league after playing extremely well to join a better league, and in the process somehow losing his ability. This can sometimes be reversed by going back to an easier league, but if the person affected is young, it is much harder.
Person 1: What happened to Jozy Altidore? He used to be so amazing.
Person 2: It's the Eredivisie effect, he joined a harder league
Person 2: It's the Eredivisie effect, he joined a harder league