Yes, it could be tricky to include this in any ruleset. As others have also mentioned, it’s very difficult for regular troops, even very well trained to fight, to handle this kind of situation. You easily end up with soldiers firing at the crowd, as happened to the French Army in Abidjan in 2004. To avoid this, the French forces in overseas deployments often include some Gendarmes who are military personal but also specially trained and equipped for riot control.
If it were allowed in the rules, players would want to do it all the time and firing above heads would become a normal way to deal with a mob – which is not realistic.