Fierce individual having row, good at heart (5)
I believe the answer is:
tiger
'fierce individual' is the definition.
'tiger' can be an answer for 'individual' (tiger is a kind of individual). I also know that 'fierce' relates to this answer.
'row good at heart' is the wordplay.
'row' becomes 'tier' (tier is a kind of row).
'good' becomes 'g' (abbreviation).
'at heart' indicates putting letters inside.
'tier' placed around 'g' is 'TIGER'.
'having' is the link.
(Other definitions for tiger that I've seen before include "Ferocious person" , "Dynamo" , "Large forest cat" , "Large feline of the forests" , "Fierce feline" .)