Recently, the government of Japan has been working on creating a society in which people enjoy participating in sports whenever, wherever, and at any age. To create such a society, there needs to be more players of all kinds of games. However, at present, more than half the public and private gyms in Japan lack instructors. In this research, we focused on the game of tennis doubles and have developed a system for improving tactics using a digital video camera even when no instructors are available. The position of each player when stroking the ball is obtained to track the player and the ball in a dynamic image. A tactic that is right for the situation and based on the positional relations of each player is presented to both the offensive and defensive side. This system can be used to encourage more people to learn to play tennis even when they cannot learn from an instructor and to build a lifelong sports society.
