Some outweigh top rowing team (5)
I believe the answer is:
eight
'rowing team' is the definition.
(I've seen this before)
'some outweigh top' is the wordplay.
'some' indicates a hidden word (some of the parts of the word are used).
'EIGHT' can be found hidden inside 'outweigh top'.
(Other definitions for eight that I've seen before include "Oxford crew, perhaps?" , "may be cut out of ice" , "Perfect cube" , "Two fours" , "Pints in gallon" .)