Case C-22/18: Judgment of the Court of Justice (Third Chamber) of 13 June 2019 (request for a preliminary ruling from the Amtsgericht Darmstadt — Germany) — TopFit e.V., Daniele Biffi v Deutscher Leichtathletikverband e.V. (Reference for a preliminary ruling — Citizenship of the Union — Articles 18, 21 and 165 TFEU — Rules of a sports association — Participation in the national championship of a Member State by an amateur athlete holding the nationality of another Member State — Different treatment on the basis of nationality — Restriction on free movement)