In the modern age of football there are many different roles and jobs a defender can have.
And a wonderful sight in the game is seeing the wing-back fly up and down the touchline terrorising the opposition.
Their role is more attacking than the full-back's, and it basically involves a great deal of running.
They are a nightmare to defend against as you never know where they're going to be.
They are usually employed in a formation that includes just three players in midfield.
This allows the wing-backs to supply all of the width in the team.
Because their job is to attack, there will usually be an extra central defender to give more defensive cover.
To be a useful wing-back, you've got to be good at all parts of the game.
Fit, strong, good with both feet, a great tackler, an amazing passer and a fine crosser of the ball.
Roberto Carlos (pictured) is never happier than when he's motoring forward for Brazil or Real Madrid.