A swat officer with acting without the knowledge of chain of command is at best an armed civilian at worst a vigilante.
In the event they shot and killed the shooter or caught anyone in the cross fire with out orders to engage they become liable for charges of murder, or man slaughter.
Tactical response groups are dangerous to be involved in and relies heavily on discipline for the protection of the team and the community they are deployed with the intent of being coordinated, if you can't be where you are expected to be you shouldn't be in swat.