As an on-ball defender, it is your job to take one side of the field away from the attacker, forcing them away from goal and not giving them a clear path to score.
Meet your attacker between the 8-meter and 12-meter arcs. As you approach the attacker, take big steps until you get close to them. Then take smaller steps to stay balanced and in an athletic position.
You want to initiate contact with the attacker with your arms locked. Remember, if you bring your arms into your body and then back out, that will be considered a foul. Use your body position to force the attacking player toward their weaker side. If they are a right-handed player, force them left by playing on their right side and taking away that path. If they’re a lefty, force them right.
As the attacker moves, position yourself so that you are not giving them any space to cut toward the goal. Keep forcing them in the direction you want them to move with your body position. You will also need to communicate with your teammates, or if another player is playing on-ball, you will need to engage in off-ball defense.
You can have better success as an on-ball defender if you can approach your attacker in a balanced, controlled manor and dictate the direction you want them to move.