Irregularity Risk of Service in Table Tennis: Taking Debatable Service of Table Tennis Women's Singles Final in 2012 London Olympic Games for Example

In Table Tennis Women's Singles Final of 2012 London Olympic Games, the penalties of Ding Ning's service not only affected the result of match but also caused debate on the service penalty. By building up two-dimensional rectangular coordinate system in the screenshots of video, locating the ball in the two-dimensional rectangular coordinate system, a quantitative research was done about toss angles and heights of Ding Ning's two services which were penalized. The results indicated that the heights Ding Ning's services were more than 40cm, and the angles were about 80 degree , reflecting that the umpire was over strict. The main reason why the umpire thought Ding Ning's toss was not vertical is the free hand moved from far to near before toss. At the same time, after projecting the ball, Ding Ning's free arm didn't remove from the space between the ball and the net which has the irregularity risk.