Tennis balls have white lines for a simple reason: to make them easier to see.
The bright white lines create a stark contrast against the yellow ball, enhancing visibility for both players and spectators. This is particularly important during fast-paced rallies, where the ball can move quickly and unpredictably.
The lines also help with tracking the ball's trajectory. Players can use the lines as reference points to anticipate the ball's path and react accordingly.
While the specific design and placement of lines may vary slightly between brands, the underlying purpose remains the same: to improve visibility and enhance the overall playing experience.
