Foolishly grow fat doing it, inspiring one’s first play (7,3,5)
I believe the answer is:
waiting for godot
'play' is the definition.
(I've seen this before)
'foolishly grow fat doing it inspiring one's first' is the wordplay.
'foolishly' indicates anagramming the letters.
'inspiring' indicates putting letters inside.
'first' indicates taking the first letters.
The initial letter of 'ones' is 'o'.
'grow'+'fat'+'doing'+'it'='growfatdoingit'
'growfatdoingit' anagrammed gives 'waitingfrgodot'.
'waitingfrgodot' going around 'o' is 'WAITING FOR GODOT'.
(Other definitions for waiting for godot that I've seen before include "Drama" , "Samuel Beckett play" .)