I love random fractures. They are the most awesome thing in ninjutsu. Especially when you and your opponent's points are very close to each other and this random fracture makes you lose.
What is the worst place to fracture? For me it's the knees because you won't be able to kick and launch towards your opponent. Kicking is very important.
Second worst place must be the wrists for me since that fracture takes away a lot if mobility.