Bet there will be no turning back — eager not to stop (6)
I believe the answer is:
yankee
'bet' is the definition.
(type of bet in gambling)
'no turning back eager not to stop' is the wordplay.
'no' becomes 'nay' (archaic form 'no').
'turning back' is a reversal indicator.
'eager' becomes 'keen' (I've seen this before).
'not to stop' means to remove the last letter.
'nay' written backwards gives 'yan'.
'keen' with its final letter taken off is 'kee'.
'yan'+'kee'='YANKEE'
'there will be' acts as a link.
(Other definitions for yankee that I've seen before include "Union soldier in the American Civil War" , "25th letter of Nato alphabet" , "A bet on multiple horses" , "Zulu comes after this" , "Informal American, a doodle dandy" .)