If you encounter the assailant, action is quicker than reaction. If the assailant is not shooting, you may decide to do what they say, although it is likely that the time for compliance and negotiation has already passed. Only you can draw the line on what you will or will not do to preserve your life or the lives of others.
If the assailant is shooting or starts shooting people, you need to make a choice, (at this point it is your choice) stay still and hope they don’t shoot you, run for an exit while zigzagging,or even attack the shooter. This is very dangerous, but certainly no more than doing nothing and dying in place. A moving target is much harder to hit than a stationary one and the last thing that the shooter will expect is to be attacked by an unarmed person(s). Any option chosen may still result in a negative consequence.
If the assailant is among your group, remember there is strength in numbers. If you and the people with you have made the decision to defend yourselves and counter the assailant then you should cause distractions to the assailant’s intended thought process.
Create as much noise as possible.
Create as much movement as possible.
Throw objects at the face of the shooter.
The goal is to increase the level of skill necessary to accurately shoot a weapon at the room occupants.
Take control of the shooter.
While distractions are conducted, one person each should grab and secure a limb of the shooter (each arm, each leg and head).
Each person should use their body weight on each limb to hold the shooter down until law enforcement arrives.
Again this is not a recommendation to attack the shooter but rather a response option to fight when there is only one other alternative.