Third down is often called the money down in football, because what happens on third down usually determines whether the offense gets a new series of downs. Which is why we talk about third-down conversion rate so much in football, and why third-down performance is such a big topic in the lead-up to games.
Heading into Sunday's game, the Cowboys have had a better third-down offense, while the Redskins have had the better third-down defense. Looking at offense and defense combined, there's not much of a difference between the two teams, as the table below shows.