The Gateway Pundit (get well Jim!) has an unusual story. It is not uncommon for a police officer to use a firearm to protect citizens. It is very rare for an armed citizen to protect an on-duty police officer. But it happened in Texas. A man had an officer pinned down and the officer could not get a clear shot. An armed citizen observed the situation and used his handgun to neutralize the threat to the officer.
You can get more details at Guns.com.