Report of name being held in reserve (4)
I believe the answer is:
bang
'report' is the definition.
(report can mean a loud noise)
'name being held in reserve' is the wordplay.
'name' becomes 'n' (common abbreviation e.g. on forms).
'being held in' indicates putting letters inside.
'reserve' becomes 'bag' ().
'n' inserted inside 'bag' is 'BANG'.
'of' is the link.
(Other definitions for bang that I've seen before include "Vigorous blow" , "Sound of explosion" , "Sudden sharp noise" , "Sudden loud noise like an explosion" , "precisely" .)