Interesting observation from a LEO:
In the verbal stage, addressing the potential BG, and instructing them along the lines of, "Hey, buddy, wait right there.", and holding up the "Stop" hand, and assessing your situation. If the BG does not appropriately respond, be more "forceful" in your address, and begin the arc. In otherwords, begin stepping off-line and lateral, as the exchange continues. This allows you to choose ground, require the BG to move, and allows you to scan the surroundings(more BG's, maybe?). His observation (and mine, when I played with it a bit), was that it makes it much harder for the BG to finalize an approach and when he does, you're in a better position to respond.