One for the record books? (5)
I believe the answer is:
clerk
'one for the record books?' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for clerk that I've seen before include "Record-keeper" , "Office/bank worker" , "Office record keeper" , "Office worker (UK) - shop assistant (US)" , "Record- or account-keeper" .)