Zion, who lost his hands and feet to a gangrene infection when he was only two-years-old became the first child to receive a double-hand transplant a year ago.
He threw out the ceremonial first pitch for the Baltimore Orioles on Tuesday.
The nine-year-old, outfitted in a custom jersey, tossed the baseball to Orioles centerfielder Adam Jones before the home game against the Texas Rangers.
Before the operation, Zion used his forearms to write, eat and play video games. Leg prosthetics also allowed Zion to walk, run and jump along with his peers.
