Rice's contention is that the league imposed a suspension of six games, then imposed a second punishment of an indefinite suspension.
And according to Rice's lawyers, the league is only allowed to impose one punishment per infraction.
It's not the punishment that is the issue so much than the second punishment that followed the first.
They suspended him for 2 games, then reacted to the @$## storm and increased it to indefinite, but the league changes suspension lengths all the time. Usually shorter, but changes are pretty standard. It’s all still one punishment.