Brother's boxing light weight doorman (7)
I believe the answer is:
bouncer
'doorman' is the definition.
(I've seen this before)
'brother's boxing light weight' is the wordplay.
'brother' becomes 'br' (abbreviation in titles of monks).
'boxing' means one lot of letters goes inside another ('box' can mean contain, as in to put in a box).
'light weight' becomes 'ounce' (I've seen this in another clue).
'br' enclosing 'ounce' is 'BOUNCER'.
(Other definitions for bouncer that I've seen before include "cheque that's worthless?" , "tough doorman" , "Security man outside night-club, or a rubber ball" , "Lively ball" , "Club doorman" .)