Man-to-man defense
The man-to-man defense (also known as personal defense) is a method used by teams to apply collective pressure on the ball. Every defender has an individual mark, a designated opponent player with who they stick. The main advantage of man-to-man defense is that it gives the coach, the ability to control over who his defenders mark. He can easily match up his own personnel according to the opponent.
Rotational system in Man-to-man marking
In the above play, Attacker 1 has just beaten Defender A. At this point (Step 1) Defender A is out of the play so his nearest teammate (B) is supposed to put pressure on the ball. The problem is that Defender B is already marking Attacker 2. Notice how Defender B positions himself so that he is covering both Attackers 1 and 2. This process buys time for the beaten Defender 1 to recover (Step 3) and pick up Attacker 2, who most likely would go forward (Step 2) once his marker has left him. Another important thing to notice is that the two far-sided defenders drop back as soon as Defender A gets beaten. This ensures that they can provide potential backup (in case Defender B gets beaten as well.)