Nervous, holding forth in loud, aggressive manner (6)
I believe the answer is:
shouty
'loud aggressive manner' is the definition.
I know nothing about this answer so I can't judge whether it can be defined by this definition.
'nervous holding forth' is the wordplay.
'nervous' becomes 'shy' (I've seen this in other clues).
'holding' means one lot of letters goes inside another.
'forth' becomes 'out'.
'shy' placed around 'out' is 'SHOUTY'.
'in' acts as a link.
Can you help me to learn more?
(Another definition for shouty that I've seen is " tending to bellow".)