More crazy one involved in strike (7)
I believe the answer is:
battier
'more' is the definition.
Although both the answer and definition are adjectives, they are not in the same form of the adjective.
'crazy one involved in strike' is the wordplay.
'crazy one' becomes 'i' (Roman numeral. I am not sure about the 'crazy' bit.).
'involved in' indicates putting letters inside.
'strike' becomes 'batter' (battering is a kind of striking).
'i' inserted inside 'batter' is 'BATTIER'.
Can you help me to learn more?
(Another definition for battier that I've seen is " More insane".)