Expert university runner, retired (4)
I believe the answer is:
guru
'expert' is the definition.
(I've seen this before)
'university runner retired' is the wordplay.
'university' becomes 'U' (abbreviation as in UMass).
'runner' becomes 'rug' (I've seen this in another clue).
'retired' shows that the letters should be reversed in order.
'u'+'rug'='urug'
'urug' reversed gives 'GURU'.
(Other definitions for guru that I've seen before include "Spiritual guide" , "Hindu or Sikh religious teacher or leader" , "Influential expert" , "Name given to the each of the first ten leaders of the Sikh religion" , "Recognised expert in some field" .)