Record-holder ran, turning on bit of gas (6)
I believe the answer is:
ledger
'record-holder' is the definition.
(I've seen this before)
'ran turning on bit of gas' is the wordplay.
'ran' becomes 'led' ('lead' can be a synonym of 'run').
'turning' shows that the letters should be reversed in order.
'on' becomes 're' ('on' can be mean 'with reference to').
'bit of' suggests taking the first letters.
The initial letter of 'gas' is 'g'.
're'+'g'='reg'
'reg' in reverse letter order is 'ger'.
'led'+'ger'='LEDGER'
(Other definitions for ledger that I've seen before include "Old accounts book" , "Book for keeping financial accounts" , "Book-keeper's book" , "Business record book" , "record-holder" .)