Alexa knows about her weakness to darkness because it cost her an important game in the past.
Alexa was rejected from the prairieville baseball team because of her inability to pitch effectively in the darkness. This resulted in her being barred from her local team despite the fact that she seems pretty good at pitching.
Newsie Moved to Mountport from to Brooklyn.
Newsie has a noticeably thick Brooklyn accent that no one else we see in the musical has. It's very likely that Newsie was born and lived in Brooklyn before he moved to Mountport. Him being relatively new to town would also explains why he is very welcoming of Alexa and gives her pointers on how to fit in.
