" Tackle " implies a running grab and throw, I'd think this is more of a generic description in the press than a accurate sequence of events. ( The Jack Ruby take down comes to mind as distance to others was near zero )
I think that if one can come up behind the shooter, using a striking object is more effective. As in the recent school board shooting, a fire extinguisher held vertically then swung in a downward motion so the base strikes the hand with the gun and gun would be more effective than a general horizontal strike.
It takes more than getting the shooter on the ground, their gun hand must be disabled.