Ferocious types start to gather in rows (6)
I believe the answer is:
tigers
'ferocious types' is the definition.
The answer and definition can be both people as well as being plural nouns.
Perhaps there's an association between them I don't understand?
'start to gather in rows' is the wordplay.
'start to' suggests taking the first letters.
'in' indicates putting letters inside.
'rows' becomes 'tiers' (tier is a kind of row).
The initial letter of 'gather' is 'g'.
'g' inserted within 'tiers' is 'TIGERS'.
Can you help me to learn more?
(Other definitions for tigers that I've seen before include "strong economies" , "Striped beasts" , "Large striped cats" , "Big striped cats poetically burning bright" , "Great striped animals, poetically burning bright" .)