A tennis racquet with a replaceable playing surface includes a frame, a cartridge, and a cartridge-lock with at least one key. The frame defines a cartridge support groove, a front upper half-oval bridge and a back upper half-oval bridge. Each bridge includes a head-guard. The front bridge with its head-guard and the back bridge with its head-guard define a planar passage way between the bridges. The cartridge includes a rim threaded with a string. The string defines a playing surface. The cartridge is shaped for removable snug fit in the support groove and in the planar passageway, such that when a replacement cartridge is snug within the frame, and when the at least one key is entered into the at least one key-aperture, the replacement cartridge is locked to the frame.