Teams displaying old power (5)
I believe the answer is:
steam
'old power' is the definition.
'teams displaying' is the wordplay.
'displaying' indicates an anagram (the anagrammed letters display the answer).
'teams' with letters rearranged gives 'STEAM'.
(Other definitions for steam that I've seen before include "Mates (anag)" , "enthusiasm" , "Driving force" , "Old-fashioned power" , "Water at boiling temperature diffused in the atmosphere" .)