The ideal situation is with as many bystanders watching as possible. That sucks if you have a gang after you, but perhaps it can be avoided in the first place by not being an easy target.
I do agree that this won’t work in all situations.
In High School, lined up waiting for an elective class, dozens of witnesses... I took this advice... I stood up to a bully, and since they were already "up in my grill" they were able to sucker punch me, right in the diaphragm, without having to raise their arm and make a big show, fist quick raise to ~90 degree bent elbow and jabbed strait forward.. leaving me struggling to stand and winded for several minutes... and because they were so close, no one clearly saw what they did... leading to dozens of people being, no witnesses at all... I changed classes.
For everyone that thinks this advice always works... some bullies aren't cowards they're worse... they are arrogant assholes that think they can get away with what they are doing, or are entitled to do it... they may not back down, and may just get worse when confronted.
I do agree that this won’t work in all situations.