Seen in massacre, winning team (4)
I believe the answer is:
crew
'team' is the definition.
(I know that crew is a type of crew)
'seen in massacre winning' is the wordplay.
'seen in' indicates the answer is hidden within the clue.
'CREW' can be found hidden inside 'massacre winning'.
(Other definitions for crew that I've seen before include "This male hair style is closely cropped" , "Sailors -- boasted" , "made triumphalist noises" , "Sailors - haircut" , "Cox and Co" .)