Beefy teams? (5)
I believe the answer is:
sides
'teams?' is the definition.
(eg football sides)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for sides that I've seen before include "Sports teams" , "Takes the part of someone in a dispute" , "More than one team" , "Opposing factions or facets" , "Teams or flat surfaces" .)