Here’s a great  explaination of the "Off Side rule".  Off Side Rule

WHAT MAKES A GOOD FORWARD OR STRIKER?

 There are different types of strikers that have the same role, but work through their own methods. Effective forwards do share some basic characteristics significant for their success:
1. Positioning – there are plenty of attackers who lack skills but score simply because of their positioning. Watch any productive striker and you will see that he can read the game quickly and anticipate plays.