A riot began before the first man returned with a large fleet (6)
I believe the answer is:
armada
'a large fleet' is the definition.
(I've seen this before)
'a riot began before the first man returned' is the wordplay.
'began' suggests taking the first letters (I've seen 'begins' mean this).
'before' means one lot of letters go next to another.
'the first man' becomes 'adam' (first man in the Bible).
'returned' shows that the letters should be reversed in order.
The initial letter of 'riot' is 'r'.
'adam' backwards is 'mada'.
'a'+'r'+'mada'='ARMADA'
'with' acts as a link.
(Other definitions for armada that I've seen before include "A great fleet, ships or planes" , "vessels" , "Large flotilla" , "Large number of ships (Spanish?)" , "The Spanish force" .)