Clack is a street tennis group based in England that is made up of tennis players that have been kicked out of tennis schools. All members of Clack are banned from entering and competiting in official tennis tournaments. The leader of Clack is Keith, and there are approximately 20 members altogether. Xiu Ling, Keith's doubles partner and possibly former co-leader, was the reason behind the formation of Clack.
The members of Clack intentionally and ruthlessly beat the tennis players of tennis schools and tennis clubs. They play with both lawn tennis balls and real tennis balls. A real tennis ball is made cloth and twine wrapped tightly around rocks or corks. It is more powerful and dangerous than a lawn tennis ball (the green/yellow balls).
UniformEditClack's uniform consists of a zipup jacket and a silver ring. The jacket is mainly black in color with the top half being red and a black stripe running down both sleeves. A gold stylized C, standing for Clack, is located on the left breast of the jacket.