Rear tire has started rubbing frame at one spot
Check the spokes - its likely one or more has broken ("I felt a shock, like a snap....".). The ones to check are ones that got from the rim, where the rubbing is occurring, to the hub on the opposite side of the rubbing (in your case, the right side of the hub). If these have let go, there is nothing stopping the rim being pulled to the left. 

It may be that these are loose, not broken, although it unlikely. If the spokes are not broken, you might be able to straighten the rim by tightening the right side spokes and if needed, loosening the left side ones. It's not too hard if the rim is not too far out of true, but needs patience for a novice. 

If there is a broken spoke, or the rim is a long way off and cannot be "tweaked" it will be worth taking to your LBS to get them to look at it. As it's only a year old, spokes should not be breaking.