A type of defender in soccer, whose primary goal is to play defense on the outer edges of the pitch, but often also has the responsibility to help in the offensive strategy. There are typically two full backs on each team, starting the game lined up outside of the centerbacks.
A fullback is a player who will be lined up defensively to start the game at the outer edges of the pitch, often only a few yards from each touchline. As the game is played, fullbacks are asked to support the attack, running forward on offense and then sprinting back on defense to support the center backs. Most fullbacks are the fastest players on the pitch, with most being stronger at either defense or offense, and elite players being great at both. They're often the players running at the edge of the pitch sending in crosses on the attack.
Fullbacks are the last line of defense before the goaltender, and they play on the wings closer to the touchline than the center backs. At the professional level, fullbacks are often rangy players that can make an overlapping run and be an offensive threat from the wing. The fullbacks main job is to defend against crosses and put pressure on plays developing from the outside channels.