A protective sleeve for a ball activated device, the ball activated device comprising a seat sleeve axially movable between an initial state in which seat defining members are configured to form a fluid tight seal with a ball and a final state in which the seat defining members are allowed to enter into a seat receiving recess such that the ball is permitted to pass. In the initial state, the protective sleeve extends axially from the seat sleeve over the seat receiving recess. The protective sleeve can be connected in the extension of the seat sleeve through a rotation lock, and ensures that particles and scaling do not build up in the seat receiving recess. The invention prevents that particles are collected behind the seat defining members and prevent these and other movable parts from moving. The protective sleeve is thus particularly suitable for applications such as cementing or fracturing.