Marcus Williams probably should have spent the 2014 season developing on the practice squad. It is debatable whether he should have been on an NFL roster, but he almost certainly should not have started eight games. Such was the state of the cornerback position for the Jets, though. Williams did get that experience. He gave up 33 catches for 348 yards. These came on 44 targets and was in coverage on 271 snaps.
These are numbers that when prorated over 16 games put him well below average, particularly when one considers some of the corners who played across from him. If there was a quality corner on the other side, teams would have made a real effort to go after Williams. It seemed like he was just trying to stay afloat. He provided plenty of cushion in an effort to avoid getting beaten deep. If you wanted a completion against him, it was almost always there. The Patriots really exploited him on a key Week 16 drive. Williams' one interception came in that game, and it was on a route where he was cleanly beaten, but Jason Babin's pressure forced a bad throw by Tom Brady.
While Williams was by no means stellar by NFL standards, by the standards of an undrafted rookie from North Dakota State, it could have been worse. He was somewhat better than the other corners on the team, many of whom had been in the NFL for years. Again, the Jets asked a lot of him just by giving him playing time before he was ready.
I don't know what the Jets have in Williams, but he was superior to the likes of Darrin Walls and Phillip Adams, and he was a rookie. I think he earned a spot in training camp to see whether he can stick as a developmental guy.