"When I fell on the couch as choreographed, I think my right hand was balled into a fist, rather than open, and that’s when I heard a crack. When I tried to hit him with my right hand, I realized something was wrong.
Supervision over non-fight violence as well as choreographed fights is also important. Knowing how to fall properly is invaluable.
http://www.playbill.com/news/article/158656-Johanna-Day-Breaks-Hand-During-Onstage-Scuffle-in-God-of-Carnage
http://www.playbill.com/news/article/158656-Johanna-Day-Breaks-Hand-During-Onstage-Scuffle-in-God-of-Carnage