He was certainly in a whole different league.

The crowd scene would be wild.

"Brosnan made one pitch, high and inside. Clemente drove it against the light standard in left field. Jim King had backed up to make the catch but it was over his head. The ball bounced off the slanted side of the fencing and rolled along the cinder path to center field. Here came Hank Foiles, Bill Virdon and then Dick Cole, heading home and making it easily. Then came Clemente into third. Bobby Bragan had his hands up-stretched to hold up his outfielder. The relay was coming in from Solly Drake. But around third came Clemente and down the home path. He made it just in front of the relay from Ernie Banks. He slid, missed the plate, then reached back to rest his hand on the rubber with the ninth run in a 9-8 victory as the crowd of 12,431 went goofy with excitement."

Thirty teams, each team playing 162 games every year since 1962 or so, 154 games every year before that since the early 1900s, not sure about the exact number but that would be more than a quarter million major league baseball games played since they started keeping records, in that many games that's bound to have happened more than just once. It seems to me, anyway.

-- Ron

An inside the park homerun is a rare enough feat, and a walk off grand slam even more so, BUT an inside the park walk off grand slam only works if the score is just right in the bottom half of last inning; play stops when a single go ahead run is scored.

Plus, the ball had to be hit by a guy so important to his team that he felt free to ignore the 3rd base coach's stop sign.
Many good players would have stopped because the coach said so, but few had Clemente's grit.
So, we need the circumstances you laid out & the right guy at the right time.