|Tennis Stuff for Brighton, Hartland, and Fenton|
Yesterday, I was watching a tennis match on TV between Andy Roddick and Roger Federer. I didn't find the match all that entertaining, since it was just a singles match, but an interesting thing happened during the second set.
Federer hit a cross-court shot for a winner. The linesman signaled that the ball was good, but Roddick challenged the call. When Shot-Spot replayed the shot, it showed that the ball had in fact touched the line. But a few seconds after the Shot-Spot graphic was removed from the screen, I realized that I had seen something that didn't look right. Fortunately for me, I had TIVO, so I quickly rewound to the scene showing the Shot-Spot replay, and just as I had suspected, the graphic showed the ball mark to be wider than the sideline. I was puzzled. The lines on the court are 2 inches wide, and the ball is 2.65 inches in diameter. Can a ball be compressed enough so that 4/5ths of its diameter touches the ground? I had to check that out.
I went out to my garage and found some black paint, a tennis ball, and a piece of white poster board. I smeared black paint all over the ball, and then wiped most of it off so that it wouldn't be too messy to handle. I laid the poster board on the ground beside my house, took a ladder and climbed up on top of the house with the black painted tennis ball.
After dropping the ball from about 20 feet high onto the white poster board, I climbed back down off my house and measured the size of the black ball mark. It had made a reasonably round mark just over 1 1/8 inch in diameter, with a few black spatters within 1/8 of an inch of the solid black circle. Being generous, I estimated that the fuzz of the ball could have touched down and made a mark of not more than 1 3/8 inch in diameter.
Before you lecture me about how a ball skids when it hits the ground on an angle, let me re-iterate that my experiment was to determine how wide the ball mark would be. I will agree that the ball mark could exceed 2 inches in length, but having performed this experiment, I am puzzled about the logic that would assume that a ball could make a mark 2 inches wide. Is there something wrong with the Shot-Spot math?
In conclusion, let me just say that I have mistrusted the technology that is used for Shot-Spot since it was first demonstrated, and this little experiment makes me even more skeptical of it's accuracy. If any of you play on clay courts, let me ask you to look at a few ball marks, and see if you don't agree that it's unlikely that you will ever see a ball mark as wide as a line.