This is inspired/based on Unknown Armies, but totally could work in most of other games.

Unknown Armies has a "Riot roll" system to determine a reaction of a crowd that witnessed an exceptional or supernatural event. It's a very straightforward system without much nuance and with a lot of handwaving. It's not very realistic either. It's essence is that you make a d2 roll, and then, if you fail it, a d100 roll, to which you apply linear modifiers "+30 if event hurt someone, -10 if event was beautiful, etc.", add 10 for every 50 people beyond a threshold of a 100, and look at the sum. If that sum is 25 or lower, a crowd stands in awkward silence and nothing happens; if that sum is 26-50, a panic begins; if it's 51+, a riot starts against a source of the event, with destructive power proportional to the score. According to this system, ANY display of magic before 10 000 people has a 50% chance to result in a dismembered mage and mob rule. ANY display. Even if that mage is literally Jesus, and the magic is a ressurection of an all-beloved philanthrope.

So, I thought up an alternative system: Crowd Reactions.

There are four common types of crowd's reaction to an exceptional or supernatural event: three stable - Panic, Riot, and Fascination; and one unstable - Confusion. When a crowd is struck by a supernatural event, three stats are assigned to it: Rage, Fear, and Admiration. As long as none of those stats overpowers other two, the crowd is considered to be in a state of Confusion. In this state, it's open to manipulation and consideration, and generally controlled by the Bystander effect. However, once a line is crossed somewhere, strong emotions start spreading through the Domino effect, and and the entire crowd turns into a force of nature.

The event reaction simulation:

0) Players whose PC's are in the crowd must declare their intentions (if any) in provoking and manipulating the crowd, and what crowd stat they want to raise by their interference.

1) The GM secretly rolls a d10 die for each of the three stats assigned to the crowd: Rage, Fear and Admiration. Stats can go above 10, but not below 0.

2) The following modifiers are then applied to the initial values of those stats:
2.1) If the event was significantly harmful to someone, GM adds 1-10 points to the Rage stat. 1 for car-scaled property destruction, 5 for a murder, 10 for the quick incineration of a school full of kids.
2.2) If the crowd is conservative, GM adds 1 point to the Rage stat.
If the crowd is uneducated, GM adds 1 point to the Rage stat.
If the crowd is aggressive, GM adds 2 points to the Rage stat.
If the crowd is in a good mood, GM subtracts 1 point from the Rage stat.
If the crowd is incapable of fighting, GM subtracts 2 points from the Rage stat.
GM may add or subtract a few additional points to the Rage stat for comparable reasons.
2.3) If the event has a large scale and/or a lot of visible power, GM adds 1-10 points to the Fear stat. 1 for a very loud unnatural sound, 5 for telekinesis of multiple cars, 10 for covering the entire visible sky with symbols of a arcane power.
2.4) GM adds 2 points to the Fear stat if there are causalities, another 2 points if the casualties are significant, and another 3 if they are massive.
2.5) If the source of event threatened the crowd, GM adds 1 point to the Fear stat if it was a success, 2 points if it was a matched success, and 3 points if it was a crit/OACOWA.
2.6) GM subtracts points from the Fear stat equal to the logarithmic size of a crowd. To calculate the logarithmic size of a crowd, take the number of digits in the crowd's size, and subtract 1 if the first digit is lower than 4.
2.7) GM adds 1-10 points to the Admiration stat if the event is beneficial to someone. 1 for opening a transport portal, 5 for ressurection, 10 for blatantly saving the world.
2.8) If the crowd is liberal, GM adds 1 point to the Admiration stat.
If the crowd is educated above average, GM adds 1 point to the Admiration stat.
If the crowd is peaceful, GM adds 2 points to the Admiration stat.
If the crowd is in a crappy mood, GM subtracts 1 point from the Admiration stat.
If the crowd consists of military men, GM subtracts 2 points from the Admiration stat.
2.9) If the event is aesthetically pleasing, GM adds 1 point to the Admiration stat. If the event is divinely beautiful, add 2 more points. If the event is ugly, GM subtracts 2 points from the Admiration stat. If the event is distributing and feels just wrong, GM subtracts 3 more points.

3) Then, the following modifiers are applied:
3.1) If the crowd has higher than average intelligence, GM adds 1-10 points to each stat. Add 1 for RPG geeks mob, 5 for a group of senators, 10 for Nobel prize laureates.
3.2) If the crowd has lower than average intelligence, GM subtracts 1-10 points from each stat. Subtract 1 point for soap opera fans, 5 points for tinfoil-hat conspiracy theorists, 10 points for clinical morons unable to live outside of asylum.
3.3) If the crowd is intoxicated, GM subtracts 1-10 points from each stat. Subtract 1 point for overdosed energy drinks, 5 points for a bottle of vodka for everyone, 10 ponts for LSD in the kool-aid.
// Explanation: Adding points to every stat flavorfully corresponds to people in the crowd considering more factors, and mechanically corresponds to lowering the probability of the crowd clinging to a stable, unreasonable behavior. Subtracting points means and represents exactly the opposite... to a certain point. That point is when crowd stats start reaching 0 - if all of them reach 0, the crowd is considered to be so out of touch with reality that it never acknowledges anything unusual and doesn't even react.

4) Then, the initial state of a crowd is determined:
If a Rage stat is equal to or higher than the sum of Fear and Admiration, the crowd will enter the state of a Riot. They will relentlessly attack the source of the event, along with whatever comes in their way. And don't expect them to calm down after they arrest, lynch or destroy the original source without a good witch hunt. They are, for a next couple hours, a force or nature - blind, brutal, and nigh-unstoppable. Expect random causalities, hustle damage, economic losses, casual arson, and a good brawl with the police.

If the Fear stat is equal to or higher than the sum of Admiration and Rage, the crowd will enter a state of the Panic. Everyone will run for their life. This is often way more dangerous than the event itself. There might be random causalities, there might be traffic chaos, and there will certainly be a hustle damage dealt to all participants. Stopping a serious panic is easier than stopping a riot, but is still a monumental task.

If the Admiration stat is equal to or higher than the sum of Fear and Rage, the crowd will enter the state of a Fascination. They will treat a source of an event as a Messiah, a Miracle Man, an opportunity for wish fulfillment. People may applause, cry tears of joy, and rush towards a the source in a way fans rush towards their idols. Any damage is unlikely, but beware - this state, while stable and self-supportive, can easily change if a source of the event will do something that will make the crowd feel betrayed. It is also, of course, the easiest (but still hard) to disperse.

If none of the above criteria are met, the crowd remains Confused for more then the first three seconds. The GM must continue to monitor the stats for it - because, if at any point in time any of the above criteria is fulfilled, the mob will turn into a corresponding state. This is the only initial state that provocations can easily change.

It's important to remember the main two principles that govern the crowd behavior: the domino effect and the bystander effect. While the crowd is calm or in the state of Confusion, the bystander effect makes it psychologically hard to act - and anyone who wants to act first, especially against the crowd, (verbal provocations don't count) must take an Isolation stress check with rank equal to the logarithmic size of a crowd. Failed check makes you unable to act instead of a usual freakout. Once the crowd enters the state of Panic, Riot, or Admiration, the Domino effect starts pushing you. In that situation, you must take the same stress check to FEFUSE to act - specifically, to refuse giving in to the mob's mood. (To calculate the logarithmic size of a crowd, take the number of digits in the crowd's size, and subtract 1 if the first digit is lower than 4.)

5) Then, the effect of the provocateurs is determined:
A provocateur is a person who acts before a crowd does, to, intentionally or unwittingly, influence the crowd.
If the crowd is in the state of Riot, all provocateurs that called to riot are followed by the people as spontaneous leaders. All provocateurs of Panic or Fascination, however, are beaten down as if they were "one of THOSE !!!"
If the crowd is in the state of Fascination, all provocateurs that called to fascination gain a good reputation in the crowd's local society. Provocateurs of Panic are calmed down by peers, and provocateurs of Riot earn themselves a bad reputation in the mentioned society.
Crowds in panic don't care about provocateurs at all.
Crowds in Confusion, however, very much do. Every successful provocation gives the crowd +1 in the attempted stat. Matched successes and crits give +2 and +3 instead. However, matched failure provocations give you a bad reputation with society of the crowd, and critical failures reduce the corresponding crowd stat by 1.
Shifting a mood of the crowd requires a specific skill, reputation, or a high risk - universal skills like Charm and Lie won't do much good.
You, of course, may roll a Hail Mary for the soul stat (a very risky roll with 1/11 chance of success compared to the normal roll.) If you have already earned a respect of a crowd, you may roll your full Soul stat instead. Skills like "Command" or "Revolutionary Struggle" can be rolled to raise Rage and provoke a Riot, skills like "Scream Like There's No Tomorrow" or "Performance" can be used to raise Fear and provoke a Panic, skills like "Preach" or "Play Along" can be used to increase Admiration and provoke Fascination. Specialized skills like "Instigation" or "Con Artist" can be used for all three.

T.b.c.