Competitor making mistake, not quite among the top people (8)

'competitor' is the definition.
(someone competing in a sports trial)

'mistake not quite among the top people' is the wordplay.
'mistake' becomes 'trip' (trip is a kind of mistake).
'not quite' means to remove the last letter.
'among' is a charade indicator (letters next to each other).
'the top people' becomes 'alist' (A-list).
'trip' with its last letter taken off is 'tri'.
'tri'+'alist'='TRIALIST'

'making' is the link.