Unexpectedly see lambs gather together (8)
I believe the answer is:
assemble
'gather together' is the definition.
(I've seen this in another clue)
'unexpectedly see lambs' is the wordplay.
'unexpectedly' indicates an anagram.
'see'+'lambs'='seelambs'
'seelambs' is an anagram of 'ASSEMBLE'.
(Other definitions for assemble that I've seen before include "See lambs (anag) - gather together" , "Collect in one place" , "Gather or collect together" , "Get together" , "Gather together in one place" .)