If you back a golfer and he doesn’t start the tournament you will have your stake refunded.
However, if the player withdraws having hit at least one shot then it will be deemed a losing bet.
There will be exceptions to both of these rules in some circumstances.
Be sure to check that individual books refund players who withdraw before teeing off.
And if the circumstances of a withdrawal are slightly unfortunate it has been known for books to court publicity and offer refunds.
Note that disqualification is also a losing bet.