Even though Ron's bones are young and healthy, they can break if they're hit very hard or if they bend at a joint too far in the wrong direction. There are different kinds of breaks. A simple fracture is when the bone breaks cleanly into two parts.
Bones also can shatter into many pieces.
A compound fracture means that a bone breaks in several pieces and some of those broken pieces stick out through the skin. All broken bones heal the same way. First, a blood clot forms in the space between the broken bones. Then bone cells begin to grow on each side of the break. The cells gradually close the gap with new bone.