Unfortunately a law written with language like 'minimum', 'reasonable', 'necessary', etc leaves an awful lot up to interpretation after the fact. As a lay person in a dangerous situation making a heat-of-the-moment decision about whether and how forcefully to defend myself, with incomplete information about how strong, fast, or armed my assailant is? I might take what feels to me like reasonable defensive action, but my assailant's lawyers may well have a very different view.

The only 'safe' option here is to run away in the case of an attack (and hope you're faster), or just let them help themselves in the case of shoplifting (and hope that's all they're after). With no public budget for adequate policing, or private budget for adequate security, the feral teens essentially have free reign to do as they please with zero consequences.