how not to grab a tanto
I've seen someone hit in the nose with a nice white oak jo when the person in front of him (all facing sensei) did a hasso movement. A bit of blood.
My worst was doing kote-gaeshi on someone attacking with a live blade (tanto). On the throw I stabbed myself in the leg - luckily the wound was only superficial.
[on unarmed injuries - I once was thrown into someone else as an Uke and hit them in the Kidney which caused them to pass out, and the most common injury I have seen is toe or finger nails being pulled out.]
However I am pleased to say that most people are very good with their Zanshin and Miai when doing weapon work with a partner and I have never seen any weapon injuries with an intentional attack.