Cliff Jumping
Cliff jumping would be relatively safe if it weren't for how accessible it is and how it's a breeding ground for people trying to one-up each other with how dangerous/extreme the stunts they conduct can be. Dozens of people die per year, but thousands of broken bones, concussions, and air-lifts to the hospital are also expected annually.
BASE Jumping
BASE stands for Building, Antenna, Span, and Earth. These are the structures that BASE jumpers seek to, well, jump off of. BASE jumping was previously the most dangerous sport of all time, but federal and state laws have dissuaded plenty of people from wanting to give it a shot. Still, about 15 people die because of it annually.