Virgin Voyages Valiant Lady Aborted Sailaway In San Juan, Puerto Rico

Here's something I've never seen a cruise ship do before: Valiant Lady began to sail away from the dock in San Juan, Puerto Rico, and then quickly returned to the pier. About an hour later, she finally did successfully sail away. I assume that there was a last-minute medical emergency that required a guest to be evacuated... but that's just a guess. I shot this time lapse video using a GoPro mounted on the railing of my balcony on Carnival Celebration, which was docked at the pier next to where Valiant Lady had been docked.