verb

spoil the appearance or quality of (something).

his reign as world champion has been blemished by controversy

mar,spoil,impair,disfigure,blight,deface,flaw,mark,spot,speckle,blotch,discolour,scar,ruin,destroy,wreck,be a blot on the landscape,disfeature,sully,tarnish,besmirch,blacken,smirch,stain,blot,taint,soil,befoul,dirty,disgrace,damage,defame,calumniate,injure,harm,hurt,undermine,debase,degrade,denigrate,dishonour,stigmatize,drag through the mud,vitiate