Large rodent, hard to handle, not keeping up like pig (7)
I believe the answer is:
porcine
'large' is the definition.
Both the definition and answer are adjectives. Maybe you can see an association between them that I don't see?
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for porcine that I've seen before include "Piggy" , "Piglike" , "Swinish" , "Piggish" , "Of pigs" .)