Last week, Jon Low at Defensive Pistolcraft posted one of his roundups of articles, videos, commentary and advice. A lot of good articles and information there, but I want to focus on several bits about liability and self-defense insurance.
Disclaimer: As always, I am not your attorney and this isn't legal advice.
Near the top of Jon's post, he discusses five questions/issues that might come up with trying to get insurance's coverage to include an armed church security team, including training, certification, and policies. These points are from a video from Michael Mann on implementing a church security team. Now, just to clarify, this is going to be for the church's liability coverage probably as part of the property or fire & casualty insurance carried by the church. Most policies should include "volunteer workers" as part of who is an insured under the policy, but you will want to make sure. The issue for the members of the security team, however, is that these are liability policies; that is, they only provide coverage (including, in most cases, a defense) for civil lawsuits filed against the insured person or organization to recover property damage or damages arising from bodily injury/death. Liability policies do not include coverage for defense against criminal charges that might be brought against the organization or the members of the church security team.
If you have homeowner's insurance, it likely includes liability coverage as well. But it may not provide coverage for work as a volunteer, and in most cases will not provide coverage if you are being paid to be part of the security team (it is, after all, homeowner's insurance, not business insurance). Again, however, there will be no coverage for defense against criminal charges.
Consequently, with this in mind, if you are part of a church security team--or more correctly, especially if you are part of a church security team--you will want to obtain self-defense protection. A little farther into Jon's post, he discusses the good and bad of various policies out there, a reasonable amount of coverage you may need, and so on. I don't want to steal his thunder, so I would advise that you just go to his post and read what he has (including a link to another post he made concerning self-defense insurance).
As to purchasing liability insurance, you should be aware that these types of policies generally only provide coverage for "occurrences," i.e., accidents. They also typically exclude coverage for intentional acts (although most also have an exception for defense of property or a person). It is possible that your insurance carrier may try to deny coverage by contending that your self-defense incident was not an "accident," so you may need to show that the need to defend yourself or others was an unforeseen, unplanned event.
As far as the amount of coverage, you obviously want enough to protect your assets. If you are "judgment proof," i.e., the value of your assets is below whatever amounts are protected from execution of a judgment, then your homeowner's policy will probably be sufficient. But if you have more assets, it may be beneficial to purchase an umbrella liability policy that will take over should the limits of your homeowner's policy be exceeded.
In any event, talk to your insurance agent or an attorney should you have questions concerning coverage or your policies.