I watched the video several times, the shooter did not trip on his own. You can clearly see some guy run at him and trip him.
Alone even armed, you are in a world of hurt. If you are going to protect your business form a militia and train.
Form a bond with your militia men so they give a sh$t about you.
Travel in groups and cover each other. This guy was alone and thus he was perceived as vulnerable so they attacked him. A larger group would have been respected.
Of course he gave much better than he got but it could have very easily gone the other way...