University Challenge, which can make a splash (4,4)
I believe the answer is:
boat race
This clue is a double definition.
'university challenge' is the first definition.
(race between Oxford and Cambridge universities)
'which can make a splash' is the second definition.
(race which takes place in water)
(Other definitions for boat race that I've seen before include "varsity match" , "Sports event" , "famous row" , "Oxford and Cambridge take part in one" , "Oxbridge contest" .)