Racing 92’s Juan Imhoff was handed a red card for a headbutt after Castres Rory Kockott was shown yellow for a bizarre tackle.
Racing 92 kept themselves in the hunt for a Champions Cup quarter-final place with a 29-7 win over Top 14 rivals Castres on Saturday.
Leone Nakarawa, Virimi Vakatawa, Dimitri Szarzewski and Louis Dupichot all went over for Racing, while Maxime Machenaud added a penalty and two conversions, and Teddy Iribaren one conversion.