>>906
Karting, car racing, unicycle jousting, golf (if you're a rich bore), trainspotting, nature photography (camping! Camp out next to some heron and wait until it catches something ― what a magnificent action shot it would make!), lollygagging.

>>908
All of these are risky and dangerous. You might catch a disease or get assaulted, or hurt yourself.

>>909
The first two might get you chased by some rabid dogs making the third a necessity. It's gravely dangerous, as you can see.

>>911
You might hurt your limbs and other organs by doing any of those.

>>913
Allergies, lack of awareness, others' ignorance are contributing to risk factors in these activities.

As you can see, my suggestions are the safest. Karting is just a jolly good fun, the worst that can happen is that you slowly bump into a short wall of tyres. Racing might require some investments, but in the end you just have to mend a car with some duct tape - and everything will be fine. Unicycle jousting demands some unicycle training and an understanding partner, but it's the safest sport in the world. And the worst that could happen on the golf course is that you might die of old age. The rest of activities are just slightly more boring than reading Wikipedia but equally safe.