  In this paper, the new two stage and postseason system of J1 League, the top
division of professional football in Japan, is simulated. Official regulation
defines that the new postseason from the 2015 season consists of five teams
selected by different principles --- the top three teams by total season
points, and the winning teams of the 1st and 2nd half of the season.
  This paper clarifies that there are overlaps within these five teams and the
average number of teams reaching the postseason is about 3.5. The probability
that the postseason is held with 3, 4, and 5 teams are estimated about 0.62,
0.35, and 0.03, respectively.
  From this result, this paper concludes that the new system of J1 League is
basically a one-stage system, whereas the new system is officially defined as a
two-stage system, due to inappropriate design of the postseason.
