The tether is attached to a base that acts as an anchor so the ball can bounce back for another volley. Simply fill the base with water or sand to counteract the movement of the ball. If it's empty, if it's empty you can take it anywhere you want to practice. Get a tennis coach now and get rid of unnecessary costs, a training partner or keep training when you stay at home. The package includes 1 x power base + 1 x extra elastic strings + 1 x tennis ball with metal connection. Product descriptions Solo Tennis Trainer Rebound Ball, Fill & Drill Tennis Trainer with Cord, Rebounder Tennis Practice Equipment Welcome to our shop. We are committed to bringing fashion and high quality items at a reasonable price for you. 24 Hour Email Online Service -If you have any questions about this item, please feel free to contact us by email. We will do our best to provide the best possible service to every customer. Instructions: If the item is fulfilled by the seller, it usually takes 9-15 days for delivery. Due to the differences in computer monitors, colors may vary slightly between the actual product and what you see on your screen. If you are not satisfied with the item or our service, please contact us in time instead of leaving negative feedback. If you have any suggestions for our products, please let us know, we will always endeavor to optimize the quality of our products.