I trained ref in sports (5,6)
I believe the answer is:
first person
'i' is the definition.
(I've seen this before)
'trained ref in sports' is the wordplay.
'trained' indicates anagramming the letters (to train can mean to grow something into a shape).
'ref'+'in'+'sports'='refinsports'
'refinsports' with letters rearranged gives 'FIRST PERSON'.
(Other definitions for first person that I've seen before include "I or we (grammar)" , "royal "we", say" , "Rebecca's written in it" , "Adam" , "was a faller at the outset" .)