I've a ball partying with drop of ale on tap (9)
I believe the answer is:
available
'on tap' is the definition.
(similar in meaning)
'i've a ball partying with drop of ale' is the wordplay.
'partying' indicates an anagram (I've seen 'parties' mean this (the letters move or party around)).
'with' is an insertion indicator.
'drop of' says to take the initial letters.
The initial letter of 'ale' is 'a'.
'ive'+'a'+'ball'='iveaball'
'iveaball' anagrammed gives 'availble'.
'availble' enclosing 'a' is 'AVAILABLE'.
(Other definitions for available that I've seen before include "Unoccupied" , "on tap" , "Free; within reach" , "Able to be obtained" , "Uncommitted" .)