That is awful.
Sadly, it's been a regular occurrence on the Fallowfield Loop in South Manchester, especially in Levenshume. I remember that a couple of years ago, after a series of attacks, the police said they didn't think the attacks were connected (same place, bike stolen, violence used, so obviously no links). However, after a recent spate, a gang of suspects is apparently awaiting trial. It's such a bloody shame because, quite apart from the basic criminality, it's a fabulous, well-surfaced route (part of the Transpennine Trail) and a great traffic-free way of crossing Manchester east to west to east (and back!)
Bastards.