For certain props and/or future (long term) bets there may be a clause stating: ‘All Bets Action’ in the header of the wager or specified under our General Sporting Events Rules.  This means that the wager will have action whether or not the contestant on whom you have bet takes part in the tournament/event.  

Even if the player does not play the bet is valid and will have action. For example: If you bet on Roger Federer to win the US Open in Tennis and the bet or header of it states:

Roger Federer (All Bets Action) 

or

2017 US Open Winner - Odds to Win - All Bets Action

Then even if he does not start/play the bet is valid and will be graded as a loss, due to the (All Bets Action) clause.