The sentence that requires semicolons instead of commas is:
The captains of the high-school softball team are pitcher, Marisa Martino, outfielder, Rachel Morrison, and catcher, Lisa Fiore.
This is because the sentence lists roles (pitcher, outfielder, catcher) along with the corresponding names. Using semicolons can help clarify the separation between the different roles and their respective names, especially if the items in the list contain commas themselves. Here's how it could be rewritten with semicolons:
The captains of the high-school softball team are pitcher: Marisa Martino; outfielder: Rachel Morrison; and catcher: Lisa Fiore.