Battered halibut's tail and drinks, including case of champagne (8)

'battered' is the definition.
The answer and definition can be both to do with contact as well as being past participle verbs.
Maybe they are linked in a way I don't understand?

'halibut's tail and drinks including case of champagne' is the wordplay.
'tail' indicates one should take the final letters.
'and' says to put letters next to each other.
'drinks' becomes 'round' (as in a round of drinks).
'including' means one lot of letters goes inside another.
'case of' suggests removing the centre (like emptying a case).
'champagne' with its centre removed is 'ce'.
The last letter of 'halibut' is 't'.
'round' enclosing 'ce' is 'rounced'.
't'+'rounced'='TROUNCED'

Can you help me to learn more?