From local NBC affiliate:

MIAMI — A passenger on an American Airlines flight told NBC 6 that shots were fired on an airplane at Miami International Airport Wednesday afternoon.
Mary Gardner, who was a guest on NBC 6’s South Florida Today show Wednesday morning, told NBC 6 a passenger on the plane caused a disturbance and an air marshal fired shots.
Miami-Dade fire rescue officials confirmed the shooting.
The Associated Press reported that the plane, American Airlines flight 924, had just arrived from Colombia and was headed to Orlando.
NBC 6’s Patricia Andreu reported that two air marshals were onboard the flight. They overheard a man speaking about a bomb and confronted the man. The man apparently tried to get off the plane and the air marshals fired their weapons.