I got the impression the original post is not asking about getting to the game, but rather what to expect the traffic to be like on the Virginia side of the Beltway over the Legion Bridge prior to the game. It shouldn't be all that bad unless there's an accident. If you have an E-ZPass you can always use the Express Lanes in Virginia if you want. They might not make much difference on a Sunday afternoon, but if the Tysons area is busy they do allow you to blow past all the slow traffic in the general lanes.
Depending on where in Montgomery County you're headed, the Beltway east of Wisconsin Avenue (MD-355) can sometimes pose a problem due to roadwork. A football afternoon can be a good time to use the Intercounty Connector to bypass some of that, again depending on where you're heading. I'd rather pay a toll and keep moving at 55–65 mph than sit in slow or stopped traffic on the Beltway.