Strongest in group takes flight, once beaten (4,2,3,6)
I believe the answer is:
king of the castle
'strongest in group' is the definition.
(the king of the castle means a powerful person)
'takes flight once beaten' is the wordplay.
'beaten' is an anagram indicator (letters beaten up or destroyed).
'takes'+'flight'+'once'='takesflightonce'
'takesflightonce' is an anagram of 'KING OF THE CASTLE'.
(Other definitions for king of the castle that I've seen before include "Chessman" , "honcho" , "move sideways in game" , "Most important person in group" .)