It was a move of desperation. The Jets were painfully thin at the cornerback position in training camp due to injuries and front office neglect. Using the always popular, "What the heck?" logic the Jets moved safety Antonio Allen to cornerback. The experiment did not go well at all. After being barely tested in the opener against Oakland, Allen went on to be one of the least effective cornerbacks in the league before being taken out of the role around midseason.
It would be easy to say the Jets messed around with a promising safety and hurt his development. It is not clear that would be accurate, though. Allen got some degree of hype for his play in 2013. He was named a starter at safety in the absence of anybody else. Playing with very low expectations, he contributed as a run stopper. He also intercepted and returned for a touchdown a Tom Brady misthrow. There were real questions about his ability in coverage, though. He was a very limited defender both in man coverage and as a zone defender. This might have played a role in the Jets eventually signing Ed Reed midseason. The Jets went on to use a first round pick on Calvin Pryor, a player who figured to in some ways render Allen's contributions obsolete.
Under these circumstances, I can understand why the Jets tried Allen out at corner. One thing he does have is a big build at 6'2 and 202 pounds. Maybe he could use his size on the outside where he would have a chance to get physical with receivers in coverage in a way a safety usually can't.
It didn't work out. Allen unsurprisingly was too raw to become an effective press corner. He could make plays in front of him, but he couldn't stick with his men. The Jets eventually moved him back to safety, but his limitations in coverage were once again exposed. Allen allowed 8 touchdowns in coverage, 4 as a corner and 4 as a safety.
After benching Allen in Kansas City, Rex Ryan gave a brutally honest explanation, "I wanted to stop somebody."
Allen's skillset just doesn't mesh with today's NFL. In another era, he might be a pretty good player. He's a solid in the box run stopper. His skills in coverage are just so limited that teams have no problem going after him. I could see bringing him to camp to see whether he might fit some subpackage if Todd Bowles gets creative. I'm not sure it would be a big deal if the Jets decided to move on, though.