SCA combat is VERY VERY safe. No one has ever sustained a serious injury doing SCA combat (caused by the combat, at least -- some people get heat stroke, but not for lack of Chirurgeons and Water Carriers shouting at them to stop before they overheat.)
While it is true that no one has suffered life-threatening injury in SCA combat, I know several people how have broken arms or ankles in Heavy combat. Duke Gaston broke his arm when a shot hit his vambrace, and I know of another gentle who broke a leg falling off a ramp storming the castle at Gulf War.
I hate to worry a mother more, but there IS risk of injury in heavy combat, which is why you have to have a signed waiver on record before you can be authorized.