The royal couple spent Saturday at a posh country club north of Los Angeles, where Prince William scored four goals in a charity polo match.
After the game, the crowd rushed the polo field despite pleas from the announcer to stay back, and security had to be brought in to keep the crowd back.
The Saturday game was scheduled as a bit of recreation during a business-packed itinerary that saw the Duke and Duchess of Cambridge arrive in California on Friday afternoon.
"My father, the Prince of Wales, and my brother, Harry, were as green as that grass outside when I told them I'd be here today," William told a reception held at the club.
"Catherine and I have had a busy few days -- so the prospect of being able to let loose this afternoon is wonderful for me."
The guests of honour arrived at the club by helicopter just after 1 p.m. local time.
William wore a white shirt and a blue blazer, while his wife wore a silver and marble grey hand-pained chinoiserie silk dress by Jenny Packham.
The venue for the match is the Santa Barbara Polo & Racket Club, which is an opulent spot about 160 kilometres northeast of Los Angeles.
For a mere $4,000 per ticket, VIP attendees got the chance to meet the royal couple and watch the match. For $400, audience members were able to watch the match from the grandstand. Proceeds will be donated to charity.
Despite the price of admission, men and women in formal attire were already streaming onto the grassy grounds by midmorning.
Reporting from Los Angeles, CTV's Tom Walters said the event was a "star-studded affair."
"This also marks the 100th anniversary of this facility, which William described as one of the great polo fields in the world," Walters added.
Other celebrities in attendance included actors Rosario Dawson, Jennifer Love Hewitt and "Titanic" star Billy Zane.
Kate presented the winning trophy to her husband's team during the finale.
Walters noted that the expensive tickets gave attendees the chance to rub shoulders with royalty, whereas the cheaper tickets do not.
"The $4,000 ticket gets you to a reception where there's a chance you can mingle."
Tomorrow, the royal couple will visit an inner city Los Angeles area and meet the public.
"By and large, since their arrival, they have attended relatively private events," said Walters, noting that Sunday's appearance should have more public access.
With a report from The Associated Press
