Know how we have a problem with our troops getting fired at by disruptors shielded from within raging mobs? How we have a problem, because once you counter-attack, the bad guys run away, or we end up hitting civilians?
Shoot one of these into one of them, with the thing constantly relaying updated GPS coordinates. When the bad guys rally after the ambush for an after-action report, well, there's where you bring the action to THEM!
Or, just sit back for several hours, and study their habits --your choice.
Why would it need to be electronic, necessarily. Why not just tag with a chemical which is easily traced by sensor and/or K9, using a soft BB size pellet so it doesn't actually damage anything and draw attention to its strike.
Interesting application, reminscent of what the authorities were trying to come up with in the riot-prone 60s.
I remember Smith & Wesson had a revolver that used .22 blanks to propel a dye-loaded slug to identify mob ringleaders. (Maybe the precursor of today's paintball guns.) They dropped the project as it was liable to kill if the wrong part of the anatomy was hit. Not a loss in my eyes if it was the right guy - I think that was the real problem, you might hit a second-rater.
Actually, it is much simpler: use a flamethrower over their heads to create a burning obstacle BEHIND the hostile crowd. The crowd starts dissipating immediately even before it is "well done". This way they are channeled, gunmen and civilians, into, should we say, a "checkpoint", where bad guys can be picked "still warm". Besides, the psychological effect (breaking the will to fight) is highly desirable.