In association football (soccer), a defender is a player who tries to prevent the other team from scoring. Association football, more commonly known as football or soccer, is a Team sport played between two teams of eleven players and is widely considered
There are four types of defender - centre back, sweeper, full back, and wing back.
The job of the centre back, centre half, central defender, or stopper is to stop opposing players, particularly the strikers, from scoring, and to bring the ball out from their penalty area. The penalty area (colloquiallly also known as the 18-yard box, penalty box or simply the box) is an area of an Association football pitch As their name suggests, they play in a central position. Most teams employ two centre backs, stationed in front of the goalkeeper. There are two main defensive strategies used by centre backs: the zonal defence, where each centre back covers a specific area of the pitch, and man-to-man marking, where each centre back has the job of covering a particular opposition player.
Centre backs are often tall, with good heading and tackling ability. An ability to read the game well is a distinct advantage. Sometimes, particularly in lower grades of football, centre backs concentrate less on ball control and passing, preferring to merely clear the ball in a "safety-first" fashion. However, there is a long tradition of centre backs having more than just rudimentary footballing skill, enabling a more possession-oriented playing style.
The position was formerly referred to as centre half, although the emphasis of the centre half was more forward thinking in action. In the early part of the 20th century, when most teams employed the 2-3-5 formation, the two players at the back were called full backs and the row of three players in front of them were called half backs. As formations evolved, the central player in this trio, the centre half, moved into a more defensive position on the field, taking the name of the position with them. The right and left players in the trio were called the right half and left half respectively.
Centre backs usually remain in the half of the field that contains the goal they are defending, but tall defenders will often go forward to the opposing team's penalty box when their team takes corner kicks or free kicks, where scoring with one's head is a possibility. A corner kick is a method of restarting play in a game of Association football. 
Notable center backs playing today include Rio Ferdinand, Nemanja Vidic, Alessandro Nesta, Carles Puyol, Fabio Cannavaro, Kolo Toure, Marco Materazzi, Jamie Carragher, Rafael Marquez, William Gallas and Lucio
The sweeper is a more versatile type of centre back that "sweeps up" the ball if the opponent manages to breach the defensive line. Rio Gavin Ferdinand (born 7 November 1978 in Peckham, London) is an English footballer. Nemanja Vidić ( Serbian Cyrillic: Немања Видић (born 21 October 1981 in Titovo Užice, Serbia, SFR Yugoslavia Alessandro Nesta, Cavaliere Ufficiale OMRI, (born March 19 1976 in Rome) is an Italian World Cup -winning footballer. Carles Puyol (born in April 13, 1978 in La Pobla de Segur, Lleida, Catalonia, Spain) is a Spanish Fabio Cannavaro, Cavaliere Ufficiale OMRI (born September 13, 1973 in Naples) is an Italian World Cup -winning footballer Kolo Habib Touré (born March 19, 1981 in Bouake) is a Muslim Ivorian footballer who plays for Arsenal. Marco Materazzi, Cavaliere Ufficiale OMRI (born August 19, 1973 in Lecce) is an Italian World Cup -winning footballer James Lee Duncan "Jamie" Carragher (born 28 January 1978 in Bootle, Merseyside) is a central defender/right-back playing his club football at Liverpool Rafael Márquez Álvarez (born February 13 1979 in Zamora Michoacán) is a Mexican football centre back and Defensive midfielder William Gallas (born 17 August 1977 in Asnières-sur-Seine) is a French international footballer of Guadeloupian descent Lucio is an Italian Male Given name ( Lucius in Latin) It may be refer to Italian people Lucio His or her position is rather more fluid than other defenders who man-mark their designated opponents. Because of this, the position is sometimes referred to as libero (from the Italian word meaning free). The sweeper's ability to read the game is even more vital than for a centre back. A sweeper is sometimes expected to build counter-attacking moves, and as such requires better ball control and passing ability than a typical centre back. However, sweepers are often merely defensive players. For example, the catenaccio system of play, used in Italian football in the 1960s, employed a purely defensive sweeper who only 'roamed' around the back line. Catenaccio is a tactical system in football with an emphasis on defence 
Some sweepers move forward and distribute the ball up-field, while others intercept passes and get the ball off the opposition without needing to hurl themselves into tackles. In modern football, its usage has been fairly restricted, with few clubs in the biggest leagues using the position.
A relatively recent innovation is the "Sweeper-Keeper" where a goalkeeper stays higher up the pitch than he might normally do, and performs the defensive actions of a sweeper by clearing long and through balls outside the penalty area. Most of these goalkeepers are fast and with some outfield skill, required if they get themselves into trouble with a poor decision to "rush out" of the penalty area. Many of these keepers are also "eccentric" which can sometimes combine to cause disastrous mistakes such as losing the ball outside the area to an opposing striker, handling the ball or fouling and being sent off or being lobbed after being too far out of the goal area. In popular usage eccentricity refers to unusual or odd Behavior on the part of an individual This style is considered to have developed as a result of the new back-pass rule in 1992. The back-pass rule refers to two clauses within Law 12 of the Laws of the Game of Association football.
The full backs take up the wide defensive positions, one on each side of the field.  Their main task is to prevent opposition players crossing or cutting the ball back into the penalty area. In some defensive systems, full backs man-mark opponents. Most full backs are also expected to provide an attacking dimension by getting upfield along the wings and providing crosses.
In the traditional 2-3-5 team formation, the two players in the final row of defence before the goalkeeper were referred to as full backs. This formation is little used in the modern game, having been replaced largely by the four-man defence, but the term "full back" lives on — the full backs now occupy the wide positions in the defensive line, with the old centre half [back] doubled-up to fill the central defensive position.
The traditional English full back was a large, strong man who would make substantial use of "hacking" - deliberately kicking the shins of opponents, a practice that was acceptable as legal in Britain but not in other countries, and caused major controversy as the game became increasingly internationalised from the 1950s on. It is now effectively banned everywhere, and it is this in part that has given rise to a different set of defensive roles.
In contrast, the role of the full back often involves an attacking element: to some extent the full backs have replaced the winger and are expected to get forward to deliver crosses from a wide position. The modern full back is usually pacy, strong in the tackle and with good stamina to get up and down the field. 
Top modern-day fullbacks include Patrice Evra, John Arne Riise, Daniel Alves, Gianluca Zambrotta, Philip Lahm, Roberto Carlos, Javier Zanetti, Gael Clichy and Sergio Ramos. Patrice Latyr Evra (born 15 May 1981 in Dakar, Senegal) is a French international footballer who plays for English John Arne Semundseth Riise (born 24 September 1980 in Ålesund) is a Norwegian football player for Roma. Daniel Alves da Silva (born May 6, 1983 in Juazeiro) known as Dani Alves, is a Brazilian footballer who plays as an attacking Gianluca Zambrotta, Cavaliere Ufficiale OMRI, (born February 19, 1977 in Como, Lombardy, Italy) is an Italian Philipp Lahm (born November 11, 1983 in Munich, Bavaria) is a German footballer who plays as a defender for Roberto Carlos may refer to Roberto Carlos (singer (born 1941 Brazilian singer Roberto Carlos (footballer (born 1973 Brazilian footballer Javier Adelmar Zanetti (born August 10, 1973) is an Argentine football defender who plays for Serie A club Internazionale Gaël Clichy (born July 26 1985 in Toulouse) is a French football player who currently plays for Arsenal of the Premier Sergio Ramos García (born March 30, 1986 in Camas, Seville, Andalusia) is a Spanish international footballer
The wingbacks are a modern variation on the full back with heavier emphasis on attack. The name is a portmanteau of "winger" and "back". They are usually employed in a 3-5-2 formation, and could therefore be considered part of the midfield. But they may also be used in a 5-3-2 formation and therefore have a more defensive role.
In the evolution of the modern game, wingbacks are the combination of wingers and fullbacks. For the Australian Rules position see Midfielder (Australian Rules. As such it is one of the most demanding positions in modern football. Wingbacks are often more adventurous than full backs and are expected to provide width in a team without wingers. A wingback 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 wingbacks.