What could cause clavicle fracture ?

Trauma: Any trauma to the chest or a fall on an outstretched arm can lead to a fracture. If there is any disease that weakens the bone, e.g. Cancer or osteogenesis imperfecta, it can fracture more easily, but some sort of force still needs to be applied to break it. This is called a pathological fracture. A clavicle does not break without having some sort of force applied to it through abuse or injury.

Fall off of bicycle: Bike accident any fall ice hockey checking blunt trauma.

Direct blow.: Typically, direct contact, such as a sports collision, or falling off a bicycle, and striking the ground with your shoulder.