Chain of three
In a chain of three, the three defenders play on one line. They have no fixed opponents. As in a chain of four , space coverage is played. The center-back and the two full- backs tend to hold back on the offensive ; in a back-four, the two full-backs perform more offensive tasks. In a system with a three-way chain, real wingers are usually played in midfield so that they can also take on defensive tasks. Diagonal balls from the opponent are a problem for this game system, as the defenders in a chain of three can cover a smaller field width than defenders in a chain of four. A big advantage of the back three compared to the back four, however, is the majority in the midfield.
The three-man chain is often confused with the defense of a libero and two man- kickers, which is still used in amateur football, as was common in professional football back then. Modern game systems, however, play with space coverage, such as a chain of three or four.