Hardest bone you can break.

I have a friend that has broken his femur. And he is only 15 years old. He plays basketball, football, and track. he did this in basketball pratice. All he did was do a crossver and the bone broke. You could hear it all over the gym. Now the doctor says the only way you can break this bone is if you are in a severly car accident. He also said this is the hardest bone you can break in your body. So how did he break it if he all he did was a crossover? The put a steel rod in his leg with a pin holding it together. Does anyone know how he copuld of broke this? and please give me some advice