There's still a lot of bitcoin sportsbook out there like jetwin,bitcoinrush and fairlay(this is a sports exchange like betfair and pinnacle). Recently Nitrogensports are just cautious with everything withdrawals and grading bets becoming too slow this is because of their sportsbook malfunctioned a couple of times where lines are up people still bet on those lines and got away with free money.
How much was in your account and did you get your money back? If not, you can put up a
scam accusation against nitrogen if you think you did nothing wrong.