if you happen to win with the $50 bet they take $50 out of the winnings and the rest is yours to keep as long as you bet how ever much you won. So say if you put $50.00 on a dog that payed $2.00 you would win $100.00
then sportsbet takes out there $50.00 so your left with $50.00
you cant withdraw that $50 until you have put $50 worth of bets on then once youve put $50 worth of bets on you can withdraw how ever much is in your account

hope that makes sense