Redskins sign former Browns guard Shawn Lauvao

[CRedskinsRule]

Washington Redskins free-agent analysis: Shawn Lauvao - ESPN

Quick analysis: He started 44 games in four seasons with Cleveland, mostly at right guard but he has played on the left side, after being drafted in the third round of the 2010 draft. He did play a variety of positions, including left guard, in college. Lauvao was not popular among Browns fans because he remains unproven, but the coaches did want him back, according to a Browns source. He's viewed as a good fit in an outside zone because of his ability to move. At 315 pounds, he has good size. But current right guard starter, Chris Chester, is only six pounds lighter.

What does "remains unproven" mean? He was in the NFC north, so went against good defenses. Did he win the battles or not? I just don't understand that.