I think Eric Smith is playing in the wrong era. In the days of the past, he could have been a star. He is physical, tough, and smart. He is an excellent run defender. The problem is the game has shifted more in the direction of the passing game with athletic tight ends. The most important ability a safety must have is arguably the ability to match up with athletic tight ends. Smith fares poorly here. This is why he has never been able to lock down a starting job full time.
He has had excellent spurts of play, but he is not the kind of guy a championship team wants to trust to handle the best tight ends in the game. The Jets used him very effectively playing underneath in early 2009 and late 2010 as almost a linebacker on passing downs. He was very good at this role. He covered better and was more athletic than an average linebacker and played the run well enough to survive in those pass heavy situations. He is not, however, a good cover guy at his natural position of safety or big or strong enough to play three downs at linebacker.
There is no question Smith is a smart player with good instincts. That is why he is a special teams weapon and the lifeline when his teammates play a game of Jeopardy. He is not, however, a full time guy. Perhaps an innovative coach will come along some day and find a scheme that maximizes the potential and accounts for the weaknesses of a linebacker-safety tweener. Do not laugh. The development of the 3-4 defense came about as teams could find hybrid pass rushers deemed too small to play end in the 4-3 and 300 pound linemen who only held the point of attack cheaply on the market. That team, however, is not the Jets under Rex Ryan.