Characteristics begin holding one back (6)
I believe the answer is:
traits
'characteristics' is the definition.
(I've seen this before)
'begin holding one back' is the wordplay.
I cannot quite understand how this works, but
'one' could be 'i' (Roman numeral) and 'i' is located in the answer.
The remaining letters 'trats' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for traits that I've seen before include "Identifying characteristics" , "Features or qualities that distinguish someone's character" , "Identifying features or qualities" , "Distinguishing features" , "Artist (anag.)" .)