Could i have a rib fracture without being struck while surfing?

Possible: Simply falling into the water could deliver enough force to break a rib, but it would be unlikely to be a severe break. Another possibility if the pain is on the front of the chest is that the junction between the rib and the cartilage could be disrupted or irritated, causing pain.

Unusually: Some stretches, pulls , falls at hitting the water at a bad angle might cause enough trauma to fracture a rib. Similarly if the rib is unhealthy for some reason, it might break with less force. Example osteoporosis.