U.S. Law Shield has an article discussing your self-defense options when trapped in a demonstration. This is not so much a discussion of what to do (although there is a bit of that), but more a discussion of your options under most state laws concerning self-defense. The primary issue, which I've noted before, is that unless your use of force is justified, using your car to strike a protester may be considered aggravated battery or battery with a lethal weapon; and even attempting to do so may result in your being charged with aggravated assault
battery/assault with a deadly weapon.
The article describes certain key factual issues that must be resolved prior to deciding to using potentially lethal force, like forcing your way through a crowd with your car:
To begin the analysis, ... we treat this situation just as we would any other use of deadly force in self-defense. Let’s start with some general concepts, and then analyze how the specifics of the law will apply in these scenarios. The concepts to focus on are imminence, reasonableness, and not being the aggressor.
Imminence. Prosecutors love to attack the imminence prong. Does a group of people blocking a roadway pose an imminent threat of death or serious bodily injury to you inside of the vehicle? Blocking a roadway, normally, cannot cause death or serious bodily injury to those inside the vehicle, much less pose an imminent or immediate threat. As a result, using a vehicle to “run them down,” or even to physically push them aside, is unlikely to be justified. However, if there is additional threatening conduct such as the protestors attempting to enter the vehicle, or say, charging toward you with a baseball bat, that is a completely different scenario. If you are placed in reasonable fear of imminent deadly force, you would be legally entitled to use deadly force in self-defense, including the use of your vehicle to neutralize the unlawful deadly force threat.
Reasonableness. What would be required to generate a reasonable fear of imminent death or serious bodily injury? The key here is that it doesn’t matter what your personal beliefs are if a jury would not believe that your fear was reasonable under the circumstances. There are extremes where your conduct will almost always be viewed as reasonable, such as attempts to set your car on fire or flip it over. On the other hand, under many circumstances, it will be extremely difficult to convince a jury that you acted reasonably if you use deadly force against protestors. One example would be injuring or attempting to injure a group of peaceful protestors who are merely blocking a roadway. If the protestors attempt, or reasonably appear to attempt, to forcibly enter blockaded vehicles, you will gain a presumption of reasonableness under the laws of many, but not all, states. You will also have a much better argument that you had reasonable grounds to fear an imminent attack with deadly force. Such conduct could include the smashing of windows or attempts to open doors. Also, you do not necessarily need to wait until the protestors have turned violent against your vehicle if you see it happening to someone else. Remember, you must have a reasonable belief from what you are seeing and hearing around you and not merely speculating about what might occur.”
* * *Not the Aggressor. Is the person seeking justification for the use of deadly force in self-defense a victim, or is he the aggressor? State laws may vary, but generally, the defense of justification is not available to the individual who starts the fight and does not stop to convey to the other person their intention to stop the aggression.
The article goes on to make some practical situations if you are faced with a group of protesters, reiterating that you cannot use your vehicle to force or "nudge" your way through the crowd. Your primary course of action, of course, is avoidance: listen to traffic reports or other services that might alert you to protests, or if you spot the crowd in time, try to turn around.
So, how might this apply in a protest or riot situation? Byington noted, “Say you are stuck for an hour in the middle of a protest and decide to ‘nudge’ one of these folks with your vehicle so that you can get out of the traffic snarl. If the otherwise peaceful protestor then becomes violent, and you use deadly force to protect yourself, a prosecutor, judge, or jury could easily argue that you were the initial aggressor. You may lose a number of legal protections, and on top of that, appear like the aggressor during the investigation or trial.
However, once the rioters attack you or attempt to enter the vehicle, the game changes, and your legal justification kicks in. With your vehicle surrounded so that you can’t escape and attackers trying to burn your car, flip it over, or attempt to drag you out of it, it is reasonable to assume that you will suffer imminent serious bodily injury or death. It is at this point you may use deadly force. In this moment of adrenaline and pure fear, you must keep your common sense. Do not get out and try to shoot your way out of the mob! You will quickly be overtaken and perhaps have your gun stripped from you. Instead, use your vehicle to get out of that situation by driving away from the surrounding rioters.
An additional point to remember is, should your vehicle come under attack, roll your windows down about half an inch. Experts say it is harder to break a window that is partly down than one that is fully closed. Turn off your ventilation system so you do not draw in any outside air in the event there is tear gas or smoke present. Further, if surrounded and moving slowly, you may want to take off your seat belt to allow a quick exit from the vehicle should it be overturned or set on fire.I have previously quoted some survival tips from Mas Ayoob on this particular circumstance which you may also want to read.