Row involving head of giant cat (5)
I believe the answer is:
tiger
'cat' is the definition.
(tiger is a kind of cat)
'row involving head of giant' is the wordplay.
'row' becomes 'tier' (tier is a kind of row**).
'involving' is an insertion indicator.
'head of' says to take the initial letters.
The initial letter of 'giant' is 'g'.
'tier' placed around 'g' is 'TIGER'.
(Other definitions for tiger that I've seen before include "Endangered carnivore" , "Ferocious person" , "Fierce, determined type" , "Carnivorous large cat" , "Beast as Shere Khan" .)