Aintree discombobulated colt (7)
I believe the answer is:
trainee
'colt' is the definition.
(colt can informally mean a new recruit)
'aintree discombobulated' is the wordplay.
'discombobulated' indicates an anagram.
'aintree' is an anagram of 'TRAINEE'.
(Other definitions for trainee that I've seen before include "As pupil" , "One learning a job" , "one needs to practice" , "Aintree (anag.)" , "21 [TYRO]" .)