Soccer players require a fully inflated ball. A fully inflated ball can be kicked farther and rolls farther. Ideally you should use a pressure gauge and inflate to the maximum pressure listed on the ball. If your pump doesn't have a gauge, if the ball has just a little give when pressed with your finger tips it is close enough. If you can't make a slight indentation with your finger tips, it's over inflated. If you can make over a half inch indentation, it needs more air. A properly inflated ball seems hard for younger players, but they're not going to hurt their foot if they are kicking properly.
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