Cricketer beginning to shine at university makes a mistake (5,2)
I believe the answer is:
slips up
'makes a mistake' is the definition.
(slipping up is a kind of making a mistake)
'cricketer beginning to shine at university' is the wordplay.
'cricketer' becomes 'slip' (position in cricket).
'beginning to' says to take the initial letters.
'at university' becomes 'up' (slang term meaning at university).
The first letter of 'shine' is 's'.
'slip'+'s'+'up'='SLIPS UP'
(Other definitions for slips up that I've seen before include "falls over" , "Makes a mistake" .)