Some lose by a mile after turning up, perhaps (5)
I believe the answer is:
maybe
'perhaps' is the definition.
('maybe' can be a synonym of 'perhaps')
'some lose by a mile after turning up' is the wordplay.
'some' says the answer is hidden in the clue (some of the parts of the word are used).
'turning up' says the letters should be written backwards.
'ebyam' is hidden in the letters of 'lose by a mile after'.
'ebyam' backwards is 'MAYBE'.
(Other definitions for maybe that I've seen before include "Perhaps, might happen" , "Perhaps, possibly" .)