Guy supervising entrance held up a form of ID (4,3)
I believe the answer is:
name tag
'a form of id' is the definition.
(a name tag identifies someone)
'guy supervising entrance held up' is the wordplay.
'guy supervising' becomes 'nam' (I can't explain this - if you can you should believe this answer much more).
'entrance' becomes 'gate' (type of entrance).
'held up' says the letters should be written in reverse.
'gate' written backwards gives 'etag'.
'nam'+'etag'='NAME-TAG'
(Other definitions for name tag that I've seen before include "Personal identification" , "Label proving ownership" , "sign of identification" , "verifies one's identity" , "One identifying" .)