You also forgot stuff like ball position and clock time that go into nfl replays as well. The way I would do it with men on base, is just have it be like a ground rule double. Maybe have a line, either in the grass or invisible, call it the double line, a certain distance from home plate where you would say if the ball landed here, the avg play would be a double. And if the disputed play happened in front of the line, then its a ground rule single, all base runners advance 1 base, and if it happens behind the line its a ground rule double and all base runners advance 2 bases. If a ball is ruled caught, but was trapped and a runner is picked off as a result then its a non-play. A base runner should not be punished for reading the play correctly, even if the ump didn't. If it's ruled not caught but was caught everyone goes back to their original base, with the exception of tagging up. Base runners aren't going to be venturing far anyway because they know it might be caught, and the ones that do are probably because there are 2 outs and its a non issue anyway. If a player would have successfully tagged up if the ruling had been correct, they get their base. It wouldn't be too hard to see that just use one of those side by side replays of the runner and fielder to see if he stayed and if hes tagged out he stays tagged out. I think that covers all scenarios, and wouldn't be all that hard to implement. The real question would be, is it gonna be like college where a booth initiates all replays, or like the nfl where the managers would get challenges? I'm in favor of having a booth controlling all the replays though. Why should a team be punished for umpires continue to blow calls in the other teams favor?