"This rivalry is caused by their anger."
Translation:Persaingan ini disebabkan oleh rasa marah mereka.
Imho the closest translation of "Persaingan ini disebabkan oleh rasa marah mereka" is "this rivalry is caused by their feeling of anger". if we omit "Rasa" it just sounds odd, in fact I can't think a sentence where "marah" is used as NOUN without "Rasa". "marah" is mostly used as an adjective. I think just memorize it as "fixed expression or one set phrase". But , you can replace "rasa marah" with "kemarahan" which is more common. I'm not really good at explaining things, I'm just a native speaker but i hope that'll help.