Coach beginning to toil, damaged in rear (7)
I believe the answer is:
trainer
'coach' is the definition.
(thesaurus)
'beginning to toil damaged in rear' is the wordplay.
'beginning to' says to take the initial letters.
'damaged' is an anagram indicator.
The first letter of 'toil' is 't'.
'in'+'rear'='inrear'
'inrear' anagrammed gives 'rainer'.
't'+'rainer'='TRAINER'
(Other definitions for trainer that I've seen before include "The odd thing an athlete may leave behind" , "Sports instructor" , "teacher" , "Soft shoe; simulator" , "Person in charge of stable" .)