[bjourne]

I'd wager it is harder for sports such as baseball and hockey. But opportunities does happen, at least in football. But ime they are ephemeral so you have to be very quick to catch them. Updating once per hour isn't nearly fast enough. For example if news get out that a player is injured and will miss a game, then the odds will shift but some bookies will be slower to react than others. That can give you a window to arbitrage for 20 minutes or so. You can do it a few times, then the bookies ban you and void all your bets.