Football only flows while the ball stays inside the white lines. The moment the whole ball crosses a boundary, play stops and a special restart begins. There are two types of boundary: the touchlines (the long sidelines) and the goal lines (the short ends behind each goal). Which line the ball crosses, and who touched it last, decides whether you get a throw-in, goal kick, or corner kick. Restarts happen dozens of times per match, so knowing the rules helps you follow the rhythm of the game instead of wondering why play suddenly paused.
⚡ DID YOU KNOW?
The whole ball must fully cross the line to be out. If even a tiny sliver of the ball is still touching the white paint, play continues. That is why TV replays zoom in so close on tight calls.