They help defend the goal, by trying to stop the other team scoring. The goalkeeper stays in the goal and the defenders are further out, trying to stop the other team getting close to the goal or getting a shot at goal. There are usually four defenders, though it is up to the manager as to how many they have. That will depend on their tactics. So they might have an extra defender or they could decide to have one less and move another player towards the middle or front of the pitch.
Another word for what the defense on a soccer team is doing is blocking. They are blocking the ball from the goal.
fullback
A back is a defender.
Neelanjan LakshmanPique
Yes, if you are a defender.
defender
fullback
Pressure of the defender
Defender...
a defender that is on the right side
Just about every team has a player with the number 5, normally a wing-defender.
The French name for a goalkeeper, such as that on a soccer field, is "gardien de but". The phrase is masculine.
The defender usually depends on the sport. In soccer (football) the defender is the one that protects the goal. I don't know much about football (American Football)
John Terry of Chelsea and England.