This happens all the time at Yankee Stadium. The way they number the sections/rows is really odd, and it screws people up. We had to make a group move from our seats one time, they went a section over to the same seats, and were moved from them because they were actually two sections down. If it's just an honest mistake I don't mind. But too many people come in and sit down closer to the field hoping no one will show up. At least wait for the latter innings. Or don't do it at all. You know the ushers can't be expected to catch everyone, and really why should they even have to? Just be decent, and sit in the seats you bought.