Off the top of my head, I can recall several, namely about a woman in the US who got paralyzed after colliding with an uke
This happened here in California. The person was warming up and another student rolled into her. It was a case of being in the wrong place at the wrong time. Stanley Pranin took a really hard line on this one but I'm not certain it wasn't just one of those stupid things that happen but then, neither he nor I, were there.
I would also add that serious injuries might not always make it into the news. For instance, I know of one case where a stroke was caused as a result of practice. A person was kicked in the throat and a day or two later a blood clot led to the stroke. I doubt many outside of the dojo ever heard about this one.
I'll just say that every year produces at least a couple of deaths from football and all things considered we are probably pretty safe.