Not an expert, but I used to religiously and obsessively play the niche sport of Gaelic/American handball, specifically the 4-wall variation.

It's essentially racquetball, but with a much smaller, much harder ball, played only with gloved hands (gloves do not pad hands, just used to keep the ball dry).

Technically the 1-wall variation might have been the first ball sport to ever exist and is certainly the predecessor to modern tennis.

Awesome game, insane workout, and one of the few sports that is truly ambidextrous (handball absolutely requires use of both hands/arms).

I had to step away when I got into the tech sector and needed to dedicate most of my time to studying and working, but I played like it was a job for 8 years. Loved it.