It's a pretty standard thing I believe in most American sports. The owners and/or the league must approve new owners. The ownership group interested in the Rams would have been better off keeping Limbaughs role a secret. Once it was out, there was very little chance enough parties were going to jump on board the idea of him owning a team.
There was an issue in MLB over the past few season where the Chicago Cubs were up for sale. One of the front runners to buy them was Mark Cuban, who also owns the Dallas Mavericks of the NBA. If you're not familiar with Cuban, he's a young (by ownership standards), very brash owner. Loved by the players, he can often be found sitting courtside and confronting officials during games, or at the very least, stirring up trouble with the league front office on a regular basis. He was basically kept from buying the Cubs by other baseball owners who did not want him coming in and shaking up their establishment.