The man entering can try again (6)
I believe the answer is:
rehear
'try again' is the definition.
('hear' can be a synonym for 'try' so perhaps 'rehear' is OK for 'try again')
'the man entering can' is the wordplay.
'the man' becomes 'he'.
'entering' indicates putting letters inside.
'can' becomes 'rear' ('rear' can be a synonym of 'can'**).
'he' inserted into 'rear' is 'REHEAR'.
(Other definitions for rehear that I've seen before include "Try again (in court)" , "Retry (a lawsuit)" , "Hold the trial again." , "be a sympathetic listener, not for the first time" .)