Wing-back
The wing-back is a modern variation on the full-back with heavier emphasis on attack. The name is a portmanteau of "winger" and "full-back". They are usually employed in a 3-5-2 formation, and could therefore be considered part of the midfield, although they may also be used in a 5–3–2 formation, in which they would have a more defensive role.
In the evolution of the modern game, wing-backs are the combination of wingers and full-backs. As such, it is one of the most physically demanding positions in modern football. Wing-backs are often more adventurous than full-backs and are expected to provide width, especially in teams without wingers. A wing-back needs to be of exceptional stamina, be able to provide crosses upfield and defend effectively against opponents' attacks down the flanks. A defensive midfielder is usually fielded to cover the advances of wing-backs.
Read more about this topic: Defender (association Football)