At the U.S. Open, they're found under the arms of every other child, the fuzzy yellow surface often covered in black scribbles from hasty autographs.
Kids tote the oversized tennis balls around the grounds of the National Tennis Center like a badge of honor. Those who have come to the Open multiple years return with the same ball, hoping to fill its exterior with signatures -- and maybe finally get their favorite player's autograph.
"Kids always have their heroes and I think that everyone wants an autograph," said Wilson Sporting Goods marketing director Tracy Almeda-Singian. "It's for getting autographs and just having something to really commemorate being here at the tournament."
The Wilson Jumbo Ball was introduced in 1990, Almeda-Singian said, and each year between 8,000 and 9,000 are sold at the U.S. Open store. This year, they're priced at $45. They sell more than any other individual item in the store, she said.
More than 1,100 were sold during last week's Arthur Ashe Kids' Day alone, Almeda-Singian said.Jackson Kemper's first trip to the U.S. Open meant he had to get a Jumbo Ball. Kemper, 14, of Leesburg, Va., already got signatures from two high-profile Americans: doubles star Bob Bryan and Ryan Harrison. On Friday he was getting in line for an autograph from No. 2-ranked Victoria Azarenka.
"I wanted to get as many autographs as I could on it," Kemper said. "It would be a great way to remember the trip."
His ultimate autograph: "I really want an Isner," Kemper said, referring to American player John Isner.
Other kids also were on the hunt, hanging around the players facilities and stalking the practice courts.
Brady Thyroff, 9, and Charlie Thyroff, 6, of Rochester, said their dream autograph would be from Roger Federer. But Friday, they waited by the practice courts for Rafael Nadal. Nadal, they said, would be a good addition to their Jumbo Balls.