Frisky mascot hard to bear (7)
I believe the answer is:
stomach
'to bear' is the definition.
(both can mean to endure or tolerate)
'frisky mascot hard' is the wordplay.
'frisky' indicates anagramming the letters.
'hard' becomes 'h' (abbreviation used in pencil classifications).
'mascot' with letters rearranged gives 'stomac'.
'stomac'+'h'='STOMACH'
(Other definitions for stomach that I've seen before include "Inside" , "stand" , "Food-processor" , "Bear - belly" , "Could Mac host this organ?" .)