I am not an umpire, and I delegate to umpires the task of determining when the infield-fly rule applies and when it doesn't. But the invocation that got the Cardinals their second out of the eighth inning seems self-evidently wrong, and it's stupendously frustrating that the outcome of the first NL Wild Card play-in game ever could depend on the incorrect application of one of baseball's least-understood rules.
Also stupendously frustrating—that the game was delayed so long because Turner Field's crowd threw trash onto the field and, according to the TBS broadcasters, at baseball players.
A single-game elimination format magnifies everything. It magnifies the stress that's inherent in the structures of baseball, the joy that comes with a win and the angst that comes with a loss. And it magnifies the anger, the group-level fury, that comes when your team gets jobbed on a weird officiating play. That's not a justification for what's happening right now; part of going to a baseball game, or out in public, is accepting implicitly that you won't allow the things you disagree with to make you into a jackass.
But the nature of this game has turned a bad call into something much more.