Only in Major League Baseball do the rosters magically multiply during the most important month of the season. While some teams simply let their September call-ups tag along to watch a postseason race unfold in person, others clear the farm system and give their prospects their first taste of MLB action.

An odd rule, yes, but one that provides fans with an exciting sneak preview of the future. 

Those fresh September call-ups will often fizzle during their big league inauguration. Some kids can’t handle the highest level of competition, and even future All-Stars typically need an adjustment period. Mike Trout hit .182 during his first September.

Other times, however, a star blossoms before our eyes. A select few All-Stars and Hall of Famers immediately announced their awesomeness upon getting a September showcase.

Now here’s where assembling this list became tricky. Is it best to throw name value aside and solely appraise raw numbers? Or would it be better to highlight the legends who dominated many more Septembers to follow?

Let’s go for both. Utility man Willie Bloomquist missed the cut despite hitting .455 in 2002, and Mike Schmidt’s .294 slugging percentage won’t allow him admission into the best all-time September call-ups either.

Not all 10 players are superstars, but some September arrivals from above-average players proved too incredible to ignore. Once those players were chosen, the actual performance matters just as much as what they later became.

And don’t worry, I’m not a biased young whippersnapper who ignored a deep lineage of baseball history. Using Baseball-Reference’s MLB Debuts page, I traveled through a century of data to ascertain the most significant September call-ups. Now because of this method, I didn’t consider players who were demoted and later brought back up during the final month.

A widely eclectic list stretching decades apart resulted from the research. Maybe next year we’ll have a new name to include on the list.

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