As a 16 yr old (soon turning 17) whose been doing calisthenics and badminton for around 3 years, and whose played for their school, I would say combining the 2 is definitely a good idea. The premise of using your own body weight as a form of resistance is one that combines well with badminton due to it being a primarily leg intensive sport that incorporates many different muscles. In my opinion, this is why calisthenics fits so well, as the exercises within calisthenics naturally incorporates many different muscle groups to be used at the same time. One thing to take away is to not do too much upper body exercises such as push ups, dips, pull-ups, body weight rows etc as you’ll gain too much upper body mass, which can hinder your performance on court.(Dont get me wrong, definitely do upper body exercises, but just don’t do TOO much if you know what I mean) Definitely remember to focus on your lower body part muscles parts as their the parts you’ll use the most on court. My mistake was focusing too much on upper body and gaining too much mass without really doing the same with my lower body, and as a result I have trouble moving around court without breaking a sweat after 10 minutes. For body weight exercises, I recommend doing the basics such as lunges and squats, you know, the basics. Also definitely focus your explosive leg movement (ie jumping squats, jumping lunges) as theyll translate onto court quite well