The duke of Cambridge played against a team that included his brother, Prince Harry, in a charity match benefiting Centrepoint, which provides services for young homeless people.
William's wife, Kate Middleton, took care of a rambunctious Prince George, who crawled on the grass in his pink overalls.
"He was in Kate's arms most of the time, but she put him down on the ground a couple of times to play," an eyewitness told Us Weekly. "He was grabbing one of the polo mallets at one point when Kate joined in with the divot stomping during a break. Kate seemed a bit nervous to let go of him though. She said, 'He's really fast!'"
George, now 10 months old, will celebrate his first birthday July 22.