The best strategy is to avoid problems in the first place. Many urban and suburbanites cannot do so easily. A firearm is usually not worth the trouble to carry — there are not many scenarios where a concealed carry can be used effectively in a public setting. You do not usually have time to draw a firearm, aim, and fire. Especially if he has a rifle and scope and you don’t see him, like in a drive by shooting. Or he pops up out of nowhere with a shotgun aimed at you. Even if he is unarmed like in a mugging, he can take your gun away from you and stolen or used against you. Better not provide him with the opportunity.
Maybe if he has a pistol you have a chance. Like if he pulls a pistol in a shopping center or movie theater. You have to either tackle him or get out of there. Fumbling for a gun will get you shot. Remember that if he has a pistol he probably cannot hit you, just like you cannot hit him. If he looks too big to tackle then get behind a wall ASAP. Throw stuff. I always wear shoes that I can run in and am quite observant of my surroundings and escape exits. I have been in numerous scary situations and frequently walk unarmed in ghettos and barrios my whole life but never had much trouble that I could not easily get out of. Or in wilderness where guns are legal and wise (learn to respect the danger of animals). It helps to be strong and coordinated.
If he has predominantly super fast twitch muscle fibers (like me) victims don’t stand a chance. Sprinters are naturally strong. If they are strong enough to catch you it is over. A gun won’t help you — he is coming too fast. That is why prevention is more important than firearms and martial arts.
I note the similarity between my shape and Usain Bolt. I have been working my calf muscles because I thought they were too skinny but see he has a skinny calf too. Maybe I am not so bad. I was the fastest in all short sprints that I ever ran in, but 100 yards is way too long for me. I max out in 20 yards and had great trouble even running moderately short distances.
By the age of 15, he had grown to 6 ft 5 in tall