Gangland boss potentially runs book when fighter boxes (2,3)
I believe the answer is:
mr big
'gangland boss potentially' is the definition.
(Mr Big can mean the leader of a criminal group)
'runs book when fighter boxes' is the wordplay.
'runs' becomes 'r' (cricket abbreviation).
'book when' becomes 'b' (abbreviation for book. I am not sure about the 'when' bit.).
'fighter' becomes 'mig' (fighter jet produced by Russian company MiG).
'boxes' is an insertion indicator (the outside letters must 'box' inside letters in).
'r'+'b'='rb'
'rb' going inside 'mig' is 'MR BIG'.
Can you help me to learn more?
(Other definitions for mr big that I've seen before include "Important man" , "chief" , "boss" , "Top man" .)