Thanks for asking! First, we will answer from the point of view of 2 members:

"Lots and lots of sports are played in Japan, so it's really, really hard to choose just one, but if I were to pick, I would say baseball for men and volleyball or tennis for women. Additionally, there are countless other popular sports like soccer, basketball, rugby, football, golf, marathon, kendo, judo, kyudo (archery), gymnastic, badminton, table tennis, swimming, surfing, sailing, mountain or rock climbing, skating, skiing and so on."

"I suppose the preferences towards sports are different between generations.
Japanese children like playing soccer and dodgeball during their break time at school. In addition, for after school activities, they often learn ones depending on their (or their parents') preferences: swimming, soccer, gymnastics, baseball, basketball, dance, ballet, karate and so on.
Regarding adults, most Japanese don't do any specific sports habitually, but they sometimes go for a walk or do exercise for their health. Or, they sometimes play badminton or play ball with their children in a park when on holiday. In addition to that, those in their 40s and older like playing golf or tennis. Moreover, Japanese women often join a mother's volleyball (team) or badminton team."

In addition, we will share results for sports from 2 surveys.

- According to the 2021 survey on Time Use and Leisure Activity (this survey was conducted by Japanese Statistics Bureau, and targeted at 10-year-olds or older), the top 10 sports Japanese do are below:
walking/light exercise (44.3%)
machine training (12.9%)
jogging/marathon (11.1%)
cycling (8.2%)
fishing (7.8%)
mountain climbing/rock climbing/hiking (7.7%)
golf (6.9%)
baseball (6.3%)
badminton (6.1%)
swimming (5.7%)

- According to an official survey in 2021 (from the Japan Sports Agency), 64% of Japanese in all age and gender enjoy walking, 15% radio calisthenics, 14% muscle training, 14% stairs workout, 13% running, 12% cycling, 7% aerobics/yoga, 6% golf, 4% climbing/trekking, 4% fishing, 4% swimming, 3% tennis, rope-jumping, badminton and bowling follow.

Finally, we will present results from 2 surveys on hobbies and activities.

- Top 10 hobbies and entertainment activities according to 2021 Survey on Time Use and Leisure Activity;
listening music (53.5%)
watch movies-not in a theater (52.7%)
playing video games or smartphone games (42.9%)
reading comics (36.8%)
reading books-without comics (31.6%)
watch movies-in a theater (29.8%)
gardening (26.0%)
taking photos and printing them (21.9%)
cooking as a hobby (19.0%)
going to an amusement park, zoo, botanical garden, aquarium, etc. (19.0%)

- This survey was conducted by Asmarq, a private company.
Men: #1:Game18%, #2:Sports 17%, #3: Reading 13%, #4: Traveling 10%, #5: Netsurfing 9%, #5: Anime/Manga 9%
Women: #1: Reading 20%, #2: Music appreciation, #3: Traveling 13%, #4: Foodie 13%, #5: Watching TV 12%, #6: Watching movie 6%, #7: Cooking 6%.

Thanks for asking and we hope this answers your questions!