Brandon Smith (Redwoodtwig)
Boffo swords are a common sight at various kinds of faires. The version I make is I think safer than some of the other designs, especially with smaller children. Heavy handed blows with this one don't hurt anywhere near as much as the ones with pvc or other more solid cores.
For the event this photo came from, we also modified some baseball masks to provide some additional protection, mainly for the smaller children. Most adults will be fine without a helmet, and in fact I've had my glasses knocked off several times and have had to stop and search for a popped out lens one time.
These will break if used too hard, which is fine. The idea is a test of skill and agility, not strength. If your fighters want to use "crowbar" style sword fighting in which size, strength and hard hitting are more important than skill or agility, then a solid oak, locust or even steel core should be used. And probably full armor should be worn.
Even so, always check them before use. Make sure the handle is still firm and in place and that a gentle bend of the "blade" doesn't reveal internal breakage. Run your hands over it to make sure any bumps are not serious. If one breaks during use, stop and replace it.