The animal, making a row, started growling inside (5)
I believe the answer is:
tiger
'the animal' is the definition.
(I've seen this before)
'a row started growling inside' is the wordplay.
'a row' becomes 'tier' (tier is a kind of row).
'started' suggests taking the first letters.
'inside' means one lot of letters goes inside another.
The initial letter of 'growling' is 'g'.
'tier' enclosing 'g' is 'TIGER'.
'making' acts as a link.
(Other definitions for tiger that I've seen before include "Carnivorous large cat" , "Formidable competitor" , "Predator" , "Dynamo" , "Endangered carnivore" .)