Grim cartoon about sport (5,6)

I believe the answer is:

motor racing

I'm a little stuck... Click here to teach me more about this clue!

'sport' is the definition.
Both the answer and definition are adjectives.
Maybe there's an association between them I don't understand?

'grim cartoon about' is the wordplay.
'about' indicates an anagram.
'grim'+'cartoon'='grimcartoon'
'grimcartoon' anagrammed gives 'MOTOR RACING'.

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