Overuse injuries can be soft tissue or hard tissue. They are a class of their own.
An example of it as a soft tissue injury would be tendonitis (for example in the shoulder or elbow). This is inflammation of one or more of the tendons surrounding a joint. Tendons hold muscles to bones, and if you think about it, using the same muscle over and over again is going to place strain on those tendons, which can lead to thickening and inflammation.
An example of a hard tissue oversue injury would be a stress fracture (for example in the shins). Runners often experience this problem when they overload their body with huge amounts of training. The body cant cope, and as a result, tiny fractures develop in the bones.
Hope that helps you!!!