Doctors treat nine men before start of the fun (13)
I believe the answer is:
entertainment
'fun' is the definition.
(I've seen this before)
'doctors treat nine men before start of the' is the wordplay.
'doctors' indicates anagramming the letters.
'before' is a charade indicator (letters next to each other).
'start of' says to take the initial letters.
The first letter of 'the' is 't'.
'treat'+'nine'='treatnine'
'treatnine' is an anagram of 'entertain'.
'entertain'+'men'+'t'='ENTERTAINMENT'
(Other definitions for entertainment that I've seen before include "show business" , "Pleasure-giving" , "Provision of hospitality" , "sport" , "Source of amusement" .)