Beaten by achievement in contract (8)
I believe the answer is:
defeated
'beaten' is the definition.
(similar in meaning)
'achievement in contract' is the wordplay.
'achievement' becomes 'feat' (feat is a kind of achievement).
'in' is an insertion indicator.
'contract' becomes 'deed' (I've seen this in another clue).
'feat' placed inside 'deed' is 'DEFEATED'.
'by' acts as a link.
(Other definitions for defeated that I've seen before include "foiled" , "Thrashed" , "Trounced" , "Vanquished" , "Whacked" .)