The purpose of this study is to examine the difference between Tag Rugby as a derivative ball game and Rugby Football in the original form. Tag Rugby was pioneered in the early 90's in England. It has been taught in primary school physical education lessons in Japan since the latter years of the 90's. Its popularity is due to the low requirement of skills necessary to participate in games, such as running with the ball and scoring points. The motive of this study examining the difference from Rugby Football is that satisfactory research has so far not been done. No study on the differenciation of Tag Rugby, without contact plays such as tackles and physical contact in Rugby Football, has been done. The analysis conducted in this study has made clear the following points. 1) The basic rules of Tag Rugby makes both the defenders and attackers play easier, the attackers can get a bigger advantage than the defenders because the ‘Tag' rule allows the attackers to continue to pass the ball. 2) One further rule of Tag Rugby, the ‘number of tags' is essential as it prevents the defenders from losing the game. 3) The biggest difference between Tag Rugby and Rugby Football is that Tag Rugby drops the phase of various kinds of ‘Contest', especially ‘Breakdown' after tackles in Rugby Football. Consequently, the ease of Tag Rugby can be explained from the view of the third point and the benefit of the activity taught in primary school PE can also be recognized.