Those Millwall heroes (5)
I believe the answer is:
lions
'heroes' is the definition.
The answer and definition can be both people as well as being plural nouns.
Perhaps there's an association between them I don't understand?
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for lions that I've seen before include "Large cats" , "Large carnivores" , "multinational tourists" , "Cats living in prides" , "Roaring cats" .)