Japan is very good at sports, at least when they decide this is going to be a focus. They were not so good nor interested in football/soccer until the 2002 World Cup was appointed to Japan and Korea and made significant investments and improvements so much so that this is now the 2nd sport in the country
Rugby is now growing with Rugby World Cup coming to Japan from this September.
Base ball remains the #1 sport here, I would interpret this comes from the huge US influence and the years of America presence, correct me if I am wrong
Although the rules remain difficult for Europeans to understand and I feel the matches are endless, (4 hours sitting on a chair!!) going to the stadium is fun, families gather, couples spend the afternoon and sing every player individual song + all sorts of anthems. you will find food, drinks, ice creams, loads of beers with lady carers. I would recommend if you have a chance, this is a place where you will meet a different side of Japan, fun, friendly and relaxed!