Not to hijack the other related thread, http://thefiringline.com/forums/showthread.php?t=436560
, tackling active shooters was brought up and Gleen E. Meyer noted correctly..
Tackle - it was also tried at Virginia Tech and the kid was shot to pieces. On the other hand in a Oregon school shooting, it worked. Have to google the details. Think the kid took a round but got to him. It does depend on distance.
Tackling is dangerous because doing so means increasing your proximity to the shooter which means the shooter may more easily be able to shoot you. It also means that you may end up with the shooter's attention focussed on you when it otherwise may not have been.
It was not terribly successful at VT as Glenn noted. It wasn't successful for Al Gratia and at least one other patron at Luby's. There is no real indication that their deaths saved the lives of any others by making their attacks. The shooter wasn't stopped or significantly delayed by the attempts and simply continued locating and shooting patrons. Gratia's daughter, however, managed to escape while the gunman was reloading - better timing.
Success in stopping a shooter is a bit of a tricky area to describe. Stopping the shooter makes it successful, one could argue, but as will be seen in the examples below, the shooter frequently isn't stopped from shooting so much as being not allowed to continue. Most of the successful active shooter stops occurred when the shooter was out of ammo, reloading, or had already voluntarily stopped. Only rarely is an active shooter stopped by being physically attacked/tackled/wrestled while still actively shooting. So the true success stories are those where the shooter had intent and means to continue the attack, but was prevented from doing so. That would be the case in the Giffords/Arizona shooting. Loughner was stopped at a point when he could not shoot, though he was trying to rectify that problem when he was clubbed over the back of the shoulders and head with a chair and tackled by the doctor who had played dead and veteran that had suffered a glancing shot to the back of his head. Loughner continued to try to load his gun while on the ground, but was stopped by the tacklers and others.
It wasn't very successful for Reagan's attempted assassination where the shooter managed to empty his revolver and struck 4 people, though Hinckley was kept from killing the President. Hinckley had to stop shooting after 6 shots because his gun was empty and as far as I can tell, he didn't have more ammo and would not have been able to reload his gun while fighting off security people. So he was captured more so than stopped.
I did a quick search for incidents where tackling has worked.
It was successful in Littleton at Deer Creek Middle School.
It worked at Kelly Elementary.
It worked at the law school shooting, though the shooter appeared done with shooting (captured, not stopped)...
Kip Kinkel was stopped by several students at Thurston High School....
...and at New York-New York Casino, stopped by off duty military reservists...
Maryville Baptist Church shooter tackled...
Another church...attempted shooting...okay it was just a BB gun but the tacklers didn't know it...
Knoxville, Tennessee church shooter tackled...
Hudson Valley Mall, tackled after running out of ammo...
Pennsylvania mall shooter tackled from behind...
Phoenix strip club shooter tackled and beaten after he ran out of ammo (captured?)...
I will stop listing examples now. Based on the information from the incidents, more often than not, shooters are stopped by unarmed folks who engage the shooter primarily through tackling/wrestling when the shooter is unable to shoot, such as when he has put his gun down (law school shooting) or out of ammo/reloading (several incidents). Cho at VT was a bit more prepared for this sort of contingency. He brough along two handguns and did not have to run out of ammo before reloading, though I don't know if that was actually the case. Like at Luby's, folks may have rushed Cho while he was shooting and he only needed to spot the attack and turn the gun on his attackers.
The Arizona folks attacked at the ideal time, when he was in the process of reloading and dealing with a bad magazine.
Unless the shooter can be attacked from behind or otherwise blindsided, rushing the shooter who is actively shooting puts the would-be hero good guys/gals at the most risk and at the greatest chance for failure. Timing appears to be critical. As hard as it may be to do for some, waiting until the shooter has to stop shooting (empty/reloading/malfunction) offers the greatest chance for success in both stopping the shooter and for the good guy/gal attackers not getting shot or killed in the attack. Similarly, it will be just as hard for many to realize and comprehend that a lull in the shooting may mean an opportunity to stop the shooter when the shooter is unable to shoot. What is most frightening here is discerning if the lull is because the shooter can't shoot or because the shooter just isn't pulling the trigger. Given the short amount of time needed to reload semi-autos or use speedloaders in revolvers, the window of opportunity may not be very big.