Defeated British eight are then eliminated nearly at the beginning (6)
I believe the answer is:
beaten
'defeated' is the definition.
(similar in meaning)
'british eight are then eliminated nearly at the beginning' is the wordplay.
'british' becomes 'b' (abbreviation e.g. in BBC).
'at the beginning' says to take the initial letters.
The first letters of 'eight are then eliminated nearly' is 'eaten'.
'b'+'eaten'='BEATEN'
(Other definitions for beaten that I've seen before include "Conquered" , "Stuffed" , "Defeated or overcome" , "Baffled" , "Defeated like whisked egg" .)