Ball guard at door (7)
I believe the answer is:
bouncer
'ball' is the definition.
(I have seen 'Lively ball' mean 'bouncer' so perhaps 'ball' could also mean 'bouncer')
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for bouncer that I've seen before include "Dance-hall employee" , "It could be a ball or a chuckerout" , "Club doorman" , "Nightclub security doorman" , "Club guard; short ball" .)