NEW YORK — Thirty minutes before the gates to Arthur Ashe Stadium opened at 4 p.m. on June 22, a cluster of people began gently rolling tennis balls across a parking lot. One after the other, they lowered one knee close to the ground, extended their opposite arm, and released a tennis ball to someone 10 feet away. Closer to a locked chain-link fence, a gaggle of people started doing calisthenics as others nervously shifted their weight back and forth, tightly clutching their paper applications.