A lamb seen jumping around a sailor (4,6)
I believe the answer is:
able seaman
'sailor' is the definition.
(able seaman is a kind of sailor)
'a lamb seen jumping around a' is the wordplay.
'jumping' is an anagram indicator.
'around' means one lot of letters goes inside another.
'a'+'lamb'+'seen'='alambseen'
'alambseen' with letters rearranged gives 'ableseamn'.
'ableseamn' enclosing 'a' is 'ABLE SEAMAN'.
(Other definitions for able seaman that I've seen before include "mariner" , "Sailor's rank" , "Senior sailor" , "Member of crew" , "Salt" .)