Volatile, I excel with bat, somehow (9)
I believe the answer is:
excitable
'volatile' is the definition.
(I've seen this before)
'i excel with bat somehow' is the wordplay.
'with' is a charade indicator (letters next to each other).
'somehow' indicates anagramming the letters.
'i'+'excel'='iexcel'
'iexcel' put after 'bat' is 'batiexcel'.
'batiexcel' with letters rearranged gives 'EXCITABLE'.
(Other definitions for excitable that I've seen before include "Highly-strung" , "Easily aroused or made emotional" , "Highly strung - easily roused" , "Volatile" , "Easily stimulated" .)