Golfer Rory admits blunder (5)
I believe the answer is:
error
'blunder' is the definition.
(I've seen this before)
'golfer rory admits' is the wordplay.
'admits' indicates the answer is hidden within the clue.
'ERROR' can be found hidden inside 'golfer rory'.
(Other definitions for error that I've seen before include "wrongdoing" , "Slip, mistake" , "Bug" , "Mistake from terrorist" , "Blunder, slip" .)