The people at the training camp in the mountains had to do special test where they had to run a special path while having tennis balls shoot at them.. In the test, Ryoma was able to hit more tennis balls at once. At the end, the path leaded to a storage cabins where there where black jerseys that looked like that ones that people in the training camp wore. The Black Jerseys then challenge court 2 at U-17 (thetvdb.com)