Ring round for beam (4)
I believe the answer is:
grin
'for beam' is the definition.
(I've seen this before)
'ring round' is the wordplay.
'round' is an anagram indicator.
'ring' is an anagram of 'GRIN'.
(Other definitions for grin that I've seen before include "Smirk" , "Accept with good grace - . . . . and bear it" , "Beam" , "Wide smile" , "Smile wryly" .)