Should be posted on their web page.
They said to check their website and social media for game delays and cancellations.
I would go to the FredNats team website first. Facebook second. Their Instagram isn't very reliable for information like that.
Their FAQs state after 5 innings are complete (4 1/2 if Nats are ahead) the game is official. If game is postponed or suspended before official then exchange can take place. I saw they updated FB about an hour ago that the game tonight July 8th is still a go. So I guess follow social media to get your updates. I have tickets for tonight's game and hoping the postpone it.
Website and social media accounts are usually updated as well.
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