Flipping the calendar to September means a number of things: the end of summer, the start of a new school year and a seemingly uncontrollable outbreak of MLB pennant race fever.

It’s also the month in which the biggest stars on teams in the midst of those races have a chance to earn their paychecks. Some will do just that, rising to the occasion and leading their teams to not only regular-season pennants but also (hopefully) postseason success.

Others will succumb to the pressure and fall flat, leading their clubs to disappointing regular-season finishes that find them watching the playoffs from the comfort of their living room couches.

Of course, a player doesn’t necessarily have to be on a contending club to have an impact on the outcomes of those races. Some will have the opportunity to rise to the occasion and play the role of spoiler down the stretch.

Here’s a look at 10 stars who will play crucial roles in deciding which teams wind up atop their respective divisions by season’s end.

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