Confirm a teetotaller holds name back (6)
I believe the answer is:
attest
'confirm' is the definition.
(to attest to something is to prove or confirm it)
'a teetotaller holds name back' is the wordplay.
'teetotaller' becomes 'tt' (abbreviation).
'holds' is an insertion indicator.
'name' becomes 'set' (I can't justify this - if you can you should give a lot more credence to this answer).
'back' says the letters should be written in reverse.
'tt' going around 'set' is 'tsett'.
'tsett' in reverse letter order is 'ttest'.
'a'+'ttest'='ATTEST'
Can you help me to learn more?
(Other definitions for attest that I've seen before include "Swear to" , "Act as witness" , "Sign on" , "Verify" , "Offer evidence" .)