Turkish referee Cuneyt Cakir (2R) shows the yellow card to Chelsea's Brazilian-born Spanish striker Diego Costa (L) after Costa clashed with Porto's Spanish goalkeeper Iker Casillas (R) during the UEFA Champions League Group G football match between Chelsea and Porto at Stamford Bridge in London on December 9, 2015. AFP PHOTO / BEN STANSALL / AFP / BEN STANSALL (Photo credit should read BEN STANSALL/AFP/Getty Images)
