Shutting off air to the engine is the quickest and easiest way to kill a motor overall.

The old finger over the stinger works in some cases but there are cases where it does not work.
If you ever experience a runaway on the track or out in the yard, have fun burning your finger off trying to plug the stinger on a car that is full throttle. Even if you can hold your finger on the stinger and tolerate the pain, it usually wont kill a runaway.

Getting the bottom of your shoe on the flywheel is another toughy when all wheels are spining and full throttle. You might as well throw the car at the ground and stomp on it.

If you dont have an air filter like the one below lets just hope the marshall on the track gets creative and kills the runaway as quickly as possible.

anytime I see a runaway this air filter is the first thing I look for, thumb over the filter and the engine is cut...quick and fast.