His cadets being naughty may be punished (9)
I believe the answer is:
chastised
'be punished' is the definition.
(similar in meaning)
'his cadets being naughty' is the wordplay.
'being naughty' indicates anagramming the letters.
'his'+'cadets'='hiscadets'
'hiscadets' anagrammed gives 'CHASTISED'.
'may' acts as a link.
(Other definitions for chastised that I've seen before include "Rebuked" , "Severely reprimanded" , "beaten" , "Sad ethics (anag.)" .)