No easy answers here, but let me try to illuminate the question.
As far as property goes, the Gemara in Bava Kama 28a says that if my neighbor fills my yard with his barrels so I'm unable to exit, I can smash a straight path from my door to the street and he can't charge me for this. However if I injure myself while doing so, I can't sue him.
This Gemara appears in the context of the permissibility of one's taking the (civil!) law into one's own hands, if one is positive that one is absolutely correct. (I am adding major disclaimers here -- ask your rabbi before trying this! Please do not get yourself arrested tomorrow and try to show the judge this website!)
Rambam thus rules (Laws of the High Court and the Punishments Entrusted to Them 2:12):
יש לאדם לעשות דין לעצמו, אם יש בידו כוח: הואיל וכדת וכהלכה הוא עושה, אינו חייב לטרוח ולהביא לבית דין, אף על פי שלא היה שם הפסד בנכסיו, אילו נתאחר ובא לבית דין. לפיכך אם קבל עליו בעל דינו, והביאו לבית דין, ודרשו ומצאו שעשה כהלכה, ודין אמת דן לעצמו--אין סותרין את דינו.
An individual may handle monetary justice himself, if he has the ability -- as he is acting entirely in accordance with the law, he is not required to bother and go to court, even if he would not lose financially by waiting to go to court. Therefore if he did so, then his opponent took him to court, and the court investigated and found that the defendant acted legally -- the courts do not overturn his justice.
Similarly the Gemara above discusses, effectively, the case of a "repo man": if your neighbor has something that is clearly and unequivocally yours, then in theory you could march in and take it back. The Gemara advises, if doing so, to pound on the door first and announce "I'm here for my car" (or whatever); if you try sneaking it at night, you could get yourself killed if you're mistaken for a thieving intruder (who we assume would kill the homeowner if the homeowner was about to call the police; as opposed to the repo man who will happily wait till the police show up and explain his case to them).
So if a Jewish court would demand that Augustine move in this situation, Benny would be allowed to move him. However if Augustine is injured in the process, Benny is liable; and if Benny injures himself in the process (let's say Augustine is just sitting there and Benny gets a hernia trying to lift him) he can't sue anyone. (The above Gemara similarly says if Augustine left a can in the middle of the road and Benny trips over it, Augustine is liable. If Benny goes out of his way to try and break the can but hurts himself in the process, that's not Augustine's problem.) That's often a problem with physical force, very often things don't turn out according to plan. (This is one of the Talmud's concerns with applying "an eye for an eye" literally, by the way.)
The last question would then be whether Jewish law would require Augustine to move. On the one hand, "hey it's public property so Augustine should be free to stand here." On the other hand, "hey it's public property so Benny should be allowed to walk here." If it's clearly a high-pedestrian-traffic area the latter would win out (plunking yourself down in the middle of the street is no different than digging a giant hole in it); if the former, I don't know. My assumption is there might be some "loitering rule" like a half-hour maximum, but that's just a guess.