When upset about anything, control becomes more undisciplined (9)
I believe the answer is:
naughtier
'more undisciplined' is the definition.
(less well-behaved)
'when upset about anything' is the wordplay.
'when' becomes 'rein' (I am not sure about this - if you are sure you should believe this answer much more).
'upset' shows that the letters should be reversed in order.
'about' indicates putting letters inside.
'anything' becomes 'aught' ('aught' means anything).
'rein' backwards is 'nier'.
'nier' placed around 'aught' is 'NAUGHTIER'.
'control becomes' acts as a link.
This may not be right. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for naughtier that I've seen before include "More mischievous" , "Less well behaved" , "More badly behaved" , "Worse" , "more unruly" .)