against Philadelphia.

Not sure where people have seen him play more games with the Redskins... maybe pre-season IDK

The one game I saw where the starting center got hurt Sullivan didn't take his place. Perhaps he wasn't active that game.
And 2015 he didn't play at all.

So I re-watched the game and I was too critical of him. I think the bottom line is that he appears to be a definite upgrade over Barnes and he knows the system. I watched the "coach's film" on NFL gamepass and it gives you the play twice at different angles.