The main difference between a fullback and a wingback is that wingbacks attack quite a lot more. These players have loads of pace, a good shot and can put in a delicious cross 9 times out of 10. For eg, Vargas, Roberto Carlos, Maicon are players that you'd typical classify as "wingbacks" because they can attack to devastating effect as well as defend, but when they do attack, someone will usually cover for them. Fullbacks, although they also need to have a good cross in them and get forward now and then, are not nearly as attacking as wingbacks. They need to be much more vigil defensively and don't take on long shots that often. 