Apple watch series 3 not registering exercise

If you're playing a sport, how do you get the Apple Watch to register it? Do you use "Other" in the exercise app. I just played Pickleball for an hour and a half, plus I walked my dog earlier in the day and the watch says I've exercised for 5 minutes. I also notice that if I walk on a treadmill, I have to swing my arm in order for the watch stats to be even close to what the treadmill says. I'm older, so I do walk quickly, but I'm not going to run on the treadmill. The stationary bike seems to be fairly accurate. It's actually a bit of a pain to have to activate an app each time, but I guess that's what you have to do.