You can't actually hear anyone from the crowd yell a version of "I got it!" but if you watch Morrison, that's the only explanation why he didn't make a play on this ball.
The pop-up drifts into foul territory towards the stands and the Marlins first baseman is the only one close enough to make a play, yet he inexplicably ducks out at the last second. Giancarlo Stanton and Ed Lucas gave pursuit but neither were close enough to consider calling him off. It had to come from someone in the stands—probably that kid yelling unintelligibly. It's been one of those nights for Miami.