This month disturbance is caused by training (11)
I believe the answer is:
instruction
'training' is the definition.
(I've seen this before)
'this month disturbance' is the wordplay.
'this month' becomes 'inst' (letter-writing abbreviation for this month).
'disturbance' becomes 'ruction' (ruction is a kind of disturbance).
'inst'+'ruction'='INSTRUCTION'
'is caused by' 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 instruction that I've seen before include "summons?" , "Training" , "Teaching" , "Teacher's job" , "Direction, order" .)