Row involving tail of big animal (5)
I believe the answer is:
tiger
'animal' is the definition.
(tiger is a type of animal)
'row involving tail of big' is the wordplay.
'row' becomes 'tier' (tier is a kind of row).
'involving' is an insertion indicator.
'tail of' says to take the final letters.
The last letter of 'big' is 'g'.
'tier' enclosing 'g' is 'TIGER'.
(Other definitions for tiger that I've seen before include "''... ... burning bright, in the forests of the night'' (Blake)" , "Predator" , "Large wild cat" , "The Celtic one has died" , "Carnivorous large cat" .)