Some psycopath let emus run with the competitor (7)
I believe the answer is:
athlete
'the competitor' is the definition.
(competitor in athletics events)
'some psycopath let emus run' is the wordplay.
'some' indicates the answer is hidden within the clue (some parts of the word are used).
'ATHLETE' is hidden in the letters of 'psycopath let emus run'.
'with' is the link.
(Other definitions for athlete that I've seen before include "One who engages in physical sports" , "Sportsman in physical contests" , "Sporting person" , "Track eventer" , "E.g. runner or jumper" .)