Even if you do not buy the conceit that ZeroRB (or modified Hybrid ZeroRB, where you select a running back in the first round and then wait until the mid-rounds to build on the position), identifying potential breakout running backs and runners who stand to gain the most from an injury in front of them is part of the skeleton key to winning your leagues.
Generally speaking, what we are looking for in Zero RB candidates are 1) pass-catching upside even without a full-time role and 2) a potential workhorse situation if the running back at the top of the depth chart was to get injured.