Soccer Positions

Here are some helpful descriptions of positions that I have found:

Defensive Positions

Defenders or backs play behind the midfielders and their primary responsibility is to provide support to the goalkeeper, and to prevent the opposition from scoring a goal. They usually remain in the half of the field that contains the goal they are defending.

The job of the center-back, also called stoppers, is to stop opposing players, particularly the strikers, from scoring, and to bring the ball out from their penalty area. Their main task is to mark the most advanced enemy forwards and fight with them in 50/50 encounters. This is the most defensively-oriented field position in soccer. Stoppers have to remain in the backline, almost at all times and usually cover the shortest distance in a match (second only to goalkeepers). Stoppers rarely get involved in offense, except in set pieces like corners and during initial buildup. 

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 mark opponents. Most full backs are also expected to provide an attacking dimension by getting up-field along the wings and providing crosses. Fullbacks get actively involved in their team's offense by staying wide, making overlapping runs and pushing up the flank.

Midfield Positions:

Midfielders are players whose position of play is midway between the attacking strikers and the defenders. Their main duties are to maintain possession of the ball, taking the ball from defenders and feeding it to the strikers, as well as dispossessing opposing players. Midfielders can be expected to cover many areas of a pitch, as at times they can be called back into defense or required to attack with the strikers. 

The outside midfielder must be very fit and is supposed to be active in both defense and offense. In defense, the he must mark the widest opponent on his flank. When he finds himself free, the outside midfielder may pinch in towards the middle while remaining on the same level with the ball. This way, he is preserving the defensive compactness of his team. In attack, the outside midfielder must stay wide, especially in the early stages of buildup. By providing width, he will stretch out the enemy defense. The outside midfielder should make supporting runs up the sideline and should be able to carry the ball.

A defensive midfielder, holding midfielder or midfield anchor is a central midfielder who is stationed in front of the back defenders for defensive reasons, thus "holding back" the freedom of the opponents to attack. The defensive midfielder screens the defense by harrying and tackling the opposition teams' attackers and defenders. They also help tactically, for instance, by directing central attacking players out to the wing where they have more limited influence, and by covering the positions of full-backs, midfielders and even the center-backs as they charge up into attack. He roams laterally from sideline to sideline, usually pressuring the ball. If any of his teammates gets beaten in the middle of the field, the defensive midfielder is expected to be first in providing backup. In offense, the defensive midfielder must stay behind the attacking line, collecting rebounds and miss-kicks. He is also expected to make supporting runs and give back pass options, especially when the ball is out, near the sideline.

An attacking midfielder is a central midfielder who is stationed in an advanced midfield position, usually behind the strikers. These players typically serve as the offensive pivot of the team, and are sometimes said to be "playing in the hole". This specialist midfielder's main role is to create goal-scoring opportunities using superior vision and skill. The attacking midfielder is an important position that requires the player to possess superior technical abilities in terms of passing and, perhaps more importantly, the ability to read the opposing defense in order to deliver defense-splitting passes to the strikers. When his team does not have possession, the center midfielder is expected to drop back and pressure the ball. In offense the attacking midfielder should be in involved in the action by making runs towards the ball.

Forward Positions:

Strikers or forwards are the players on a team in the row nearest to the opposing team's goal. The primary responsibility of strikers/forwards is to score goals. Other duties can include setting up goals for other players (usually another forward, but sometimes midfielders as well) and holding the ball up so that other players may join the attack. The job of the forward is not merely to head for goal every time he receives the ball. He must also make runs towards his own goal and support the midfield rather than simply rush forward. Whenever a team is playing with two forwards, they must both move in conjunction. If the ball is on the left flank for example, they must shift towards it so that one of them is in the center and the other near the sideline. By keeping the distance between each other constant, forwards can work the ball effectively while pulling apart the enemy defense.