Pack calling for someone, going berserk (9)
I believe the answer is:
rampaging
'going berserk' is the definition.
(going berserk means rampaging or rioting)
'pack calling for someone' is the wordplay.
'pack' becomes 'ram' (synonyms).
'calling for someone' becomes 'paging' (paging someone is calling them).
'ram'+'paging'='RAMPAGING'
(Other definitions for rampaging that I've seen before include "Rushing wildly around" , "Running riot" .)