There was an article on Cycle Oregon sometime in winter about some local cyclists that had been caught in boobytraps recently. The two I remember both were on commuter bike lanes. In one situation someone had placed a ring of large rocks in the bike lane and covered it with leaves. That caused a nasty wreck, I don't remember the specifics though. The other traps I rember was one of the neck wires. The biker was moving rather fast, so it probably would have been fatal, but it just happened at the time that the biker was off the bars and upright. The wire caught the biker in the chest and sent her to the hospital.
The worst kind of coward set these up.