Half of undergrads perhaps displaying an earring? (4)
I believe the answer is:
stud
'an earring?' is the definition.
(I've seen this before)
'half of undergrads perhaps' is the wordplay.
'half of' means to take half the letters.
'undergrads perhaps' becomes 'students' (undergrad is a kind of student).
'students' cut in half is 'STUD'.
'displaying' is the link.
(Other definitions for stud that I've seen before include "Virile man" , "Boss; shirt fastener" , "who believes he can keep it up" , "kind of farm" , "Collar button or horse farm" .)