Mark Sanchez is one of those players whose negatives have come to define him. We forget that he was a first-round pick, that he went to the AFC Championship Game in each of his first two seasons. We associate him with the butt-fumble, with bad interceptions, with the futility that is the New York Jets. When his name is suggested in connection with your favorite team, your first reaction is something along the lines of, "Jeez. Really? Why?"

But the fact is, at this point in his career, Sanchez is everything you look for in a backup quarterback. And that's what the Philadelphia Eagles see in him -- a backup quarterback. The Eagles signed Sanchez to an undisclosed contract on Thursday. He's not being brought in to compete with Nick Foles, whose monster second half of the 2013 season solidified him as the team's starter going into 2014. It's possible that Sanchez is being brought in to compete with second-year man Matt Barkley for the backup role, but since Barkley was and likely still is a project, it's also possible that Sanchez is being brought in to serve as Foles' backup until (or if ever) Barkley is ready to do that.

Would Chip Kelly's offense function as smoothly with Sanchez at quarterback as it did last year with Foles? Unlikely, if Sanchez were to be as inaccurate a thrower as he has been so far in his career. But that's not the point. Very few teams have ever had a backup who could step in and replicate a starter's performance, because quarterbacks who can do that tend to get jobs as starters elsewhere. The job of a backup quarterback is basically to not mess things up. And Sanchez has enough NFL experience to allow Kelly to believe he can meet that standard.

What you're looking for in a backup is a guy for whom the moment won't be too big -- a player who won't fall apart emotionally just because he suddenly finds himself thrown into an NFL game. Sanchez fits that description. There are only seven active NFL quarterbacks (and only 36 in league history, for that matter) who have won more playoff games than the four Sanchez won in his first two seasons. Of the backup options on this offseason's market, the only one with more experience as a starter was Michael Vick, who coincidentally just left the Eagles to sign with the Jets.

If something happens to Foles and he has to sit out a couple of plays or a quarter or a game or a few weeks, Sanchez gives Kelly the ability to put a quarterback into the game who's not going to be overwhelmed. And there's peace of mind in that. Sanchez might not play well, and the Eagles might struggle if they have to go with him for a few weeks, but the same can be said for any backup anywhere.

The best-case scenario for Sanchez in all of this is that he gets an opportunity at some point to put on a positive performance and rebuild his career as an NFL starter. But if all he's going to be is a backup, the fact that he used to be a starter makes him a valuable one.