A recent news item indicates Tokyo's Jingu Stadium may be closed from May to October in 2020 because of the Olympic Games. I am not certain why it has to be closed for five months but can understand.
Since the ballpark is located adjacent to the National Stadium where the Olympics will be held, it needs to be shut down at some point prior to the start of the Summer Games for security reasons and to alleviate congestion in the area.
The 2020 Olympics are scheduled for July 24-Aug. 9, followed by the Paralympics (Aug. 25-Sept. 6).