I'll let you go first on running a kickoff back against NFL guys. I used to return kickoffs and punts in high school and personally I hated it especially punts. I was under a punt one time and a meth baby blasted me full speed before I even caught the ball. It was a penalty but I was still injured at that point.
The other thing about getting the shot to do something like that and getting an accurate experience to see how good they are is a person would have to be training for months and months and not just be going in their cold turkey. Like even if someone played in the MLB and didn't see a live pitch for a week and stepped up to the plate their chances at success are extremely low. That is why when guys get hurt they usually send them even clear down to single A to get their timing back against live pitching and often what you will find is they don't actually do that well down there. It isn't like they go down and just start crushing bombs and averaging .400 So it certainly becomes a question of how much of a diffrence is there even between the different levels of professional baseball.
The thing that always pissed me off with the new version of the American Gladiators was that they would always have the contestants be like 5'7" 130lb so the Gladiators would look super human against them. They typically didn't have formatable competition. Same thing sometimes with that Joe's VS Pro's type stuff. Like of course a top level athlete is going to destroy a weekend warrior who has a gut but what happens when they go against someone who was a college athlete who just graduated or something but didn't get drafted for whatever reason. I know people don't identify with that as much but I think a lot of those shows build it up like that the pros are god like. Don't get me wrong, sometimes they are but not the exact way it is built up like on TV.
Also everytime I see some video online where some legit basketball player or something is playing a "regular guy" they destroy them but often times the person they were playing wasn't any good anyways. Like I can go to LA Fitness and pick out 8 of the guys I play with and they would do better than the guys that we see in some of these videos. Some Somali Pirate played Kobe in this video.
I'm not going to lie. I could do better than this guy against Kobe. Of course Kobe would still win from size advantage and skill but at least I wouldn't be jumping on his back trying to hug him like that guy was.