| 摘要 |
Balls are provided to train someone to throw with proper rotation. A marking is positioned on the ball to enhance viewing of rotation. The marking is in a contrasting color than the rest of the cover and covers at least a quarter of the outer surface of the ball. The stitches are colored to avoid interfering with the visual effect of the marking, such as having stitches with similar coloration to the non-marking portion of the ball. Balls with different amounts or designs of marking may be used to train in stages. For example, a kit of balls for different stages is provided. The balls of different stages require different rates of rotation to appear visually similar to each other when thrown properly.
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