Sport involving power a lot (5,4)
I believe the answer is:
water polo
'sport' is the definition.
(water polo is a kind of sport)
'involving power a lot' is the wordplay.
'involving' indicates anagramming the letters.
'power'+'a'+'lot'='poweralot'
'poweralot' is an anagram of 'WATER-POLO'.
(Other definitions for water polo that I've seen before include "Team sport with wet participants" , "Game played by teams of swimmers with large ball" , "Sport for swimmers" , "Game played by swimming teams with large ball" , "Game played by tams of swimmers with large ball (5.4)" .)