The 4-3-3

Positioning
The standard 4-3-3 employs four fullbacks, three midfielders, and three forward players. Among the fullbacks, two are center halves (playing together in central defense) and two are wide defenders (sometimes wing-backs) to the right and left of the center halves. Typically, the outside fullbacks are in more advanced positions than the two center halves. The three midfielders are arranged in an inverted triangle shape with two higher up the field and the third in a "holding" position in the space in front of the center halves. Among the three forward players, one (the center forward) plays in a more advanced central position and the other two play to the right and the left of the center forward, often in very wide positions.

Attacking Philosophy
The 4-3-3 generally is used by more aggressive, attack-minded teams. In the attack, the center forward (the "9") is used as a high target for the midfielders with the right and left forwards making attacking runs into gaps in the opposing defense based on the movement and possession of the center forward. The highest midfielders serve as support for the forwards and have ball possession and distribution as their primary responsibilities. The holding midfielder (the "6") is the main connection between the fullbacks and the attacking players. Distribution and switching the attack from one side to the other (or from one side to the middle of the field) are the primary responsibilities of the holding midfielder. The center halves serve as support in the attack. Like the holding midfielder, the center halves often work to move the focus of the attack in possession. The outside fullbacks are responsible for widening the field in order to open as much space as possible for the attack by moving into very wide positions. The outside fullbacks also make attacking runs along the wings to add more options for the attack, to send crosses into the box, and to put more pressure on the opposing defense. 

Strengths
When played well, the 4-3-3 creates a great deal of pressure for the opposition. It is a very effective formation against an opposition without strong ball possession or with slower fullbacks.

Weaknesses
Because it is such an aggressive formation and relies on many players higher up the field, the 4-3-3 is vulnerable to counterattacks. Loss of possession in the midfield can leave the fullbacks outnumbered in defense.

When to Employ the 4-3-3
The 4-3-3 is effective for teams with intelligent, speedy players and skilled fullbacks. Teams with strong ball possession often play the 4-3-3 well.

Derivatives of the Standard 4-3-3

The False 9
The False 9 is a 4-3-3 in which the center forward (the "9") plays deeper than the outside forwards. The center forward has more ability to make runs and find space behind the outside forwards. In a False 9 formation, the attacking midfielders more often make runs into spaces higher up the field and act as extra forwards as the center forward assumes a more distributional role.

The Number 10 (the Defensive 4-3-3)
The Number 10 is a 4-3-3 in which the midfielders are arranged in a standard (as opposed to inverted) triangle shape. The midfielder at the top of the triangle (in the most advanced position) is known as the "10." The "10" plays just behind the forwards and serves as the focal point of the attack, distributing to the more advanced players or making attacking runs for shots on goal. An effective "10" typically is a player of very high skill, intelligence, and fitness. The basic philosophy of this version of the 4-3-3 is to maximize the ability of the most talented player on the team to affect the course of the game.