Consequently, rambunctious leader issues line which leads to regret (6)
I believe the answer is:
sorrow
'to regret' is the definition.
(I've seen this in another clue)
'consequently rambunctious leader issues line which leads' is the wordplay.
'consequently' becomes 'so' (synonyms).
'rambunctious leader issues' becomes 'orr' (I can't explain this - if you can you should give a lot more credence to this answer).
'line' is an insertion indicator.
'leads' says to take the initial letters.
The first letter of 'which' is 'w'.
'so' enclosing 'orr' is 'sorro'.
'sorro'+'w'='SORROW'
Can you help me to learn more?
(Other definitions for sorrow that I've seen before include "Expression of grief" , "trial?" , "Misery" , "Sadness; one magpie for it" , "Sadness, feeling of regret" .)