Indulgent, allowed nine to run in (7)
I believe the answer is:
lenient
'indulgent' is the definition.
(I know that indulgent can be written as lenient)
'allowed nine to run in' is the wordplay.
'allowed' becomes 'let' (to let is to allow or permit).
'to run' indicates an anagram.
'in' indicates putting letters inside.
'nine' anagrammed gives 'nien'.
'let' placed around 'nien' is 'LENIENT'.
(Other definitions for lenient that I've seen before include "Soft on the rules" , "Forgiving, soft" , "Mild and tolerant" , "Compassionate" , "Tolerant, merciful" .)