First of contenders, or enemy beaten — formality (8)
I believe the answer is:
ceremony
'formality' is the definition.
(ceremony is a kind of formality)
'first of contenders or enemy beaten' is the wordplay.
'first of contenders' becomes 'c' (1st letter of 'contenders').
'beaten' is an anagram indicator (letters beaten up or destroyed).
'or'+'enemy'='orenemy'
'orenemy' with letters rearranged gives 'eremony'.
'c'+'eremony'='CEREMONY'
(Other definitions for ceremony that I've seen before include "Pomp and 6" , "Ritualised public occasion" , "formal public occasion" , "Ritual celebration" , "Ritual - my encore (anag)" .)