Opinion of Advocate General Tanchev delivered on 7 March 2019.#TopFit e.V. and Daniele Biffi v Deutscher Leichtathletikverband e.V.#Request for a preliminary ruling from the Amtsgericht Darmstadt.#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.#Case C-22/18.