WW2 leader some competitor (4)
I believe the answer is:
tito
'ww2 leader' is the definition.
(Josip Tito)
'some competitor' is the wordplay.
'some' indicates the answer is hidden within the clue (some of the parts of the word are used).
'TITO' is hidden within 'competitor'.
(Other definitions for tito that I've seen before include "Marshall ..., President of Yugoslavia from 1953" , "Revolutionary" , "President of Yugoslavia, 1953-80" , "Former Yugoslav dictator" , "Josip Broz pseudonym" .)