A 29-year-old manager, Daniel Hermann, will help Andreas Rudolf to run the German Sport 2000 organization from next Jan. 1. Acting as joint managing director, he will take the position formerly occupied by Rolf Gross, who left last February. Michael Decker, an executive of the sister company ANWR Schuh, has been filling it in on an interim basis. Hermann has been working most recently at the Metro Group in various roles, most recently in charge of customer service and in sales. He has been responsible for budget planning at Metro Cash & Carry's German operations, getting involved also in strategic planning and sales development. As one of his students in international commercial management, Hermann had previously made a strong impression on one of his teachers, Günter Althaus, chief executive of the ANWR Group, the cooperative that runs Sport 2000 in Germany. Nearly 1,000 sporting goods stores are affiliated with the German buying group.