When a drive is knocked or has a power fluctuation the heads can impact the platters and cause a “head crash” in some situations this will just be a glancing blow and the heads are damaged slightly and need replacing. In worse case situations it will cause the heads to be ripped off and scratches to the platters.
On the picture above we have an example of a head crash which has caused a true “Sticktion”, this is a phrase used by data recovery technicians to describe the heads being stuck to the platters often preventing a drive from spinning if still fastened to the head stack assembly, much like a brake disk and pad on a car.
The picture shows that the heads not only landed on the platter but also stuck to the surface and ripped free of the slider.
In this case becoming an obstruction to any new heads passing over that area and requiring delicate micro surgery to lift the head away from the platter without increasing the surface damage.
The shearing force created by the rotational speed of the platter was sufficient to pull the head off the head stack slider but not enough to fling the head off to the sides or cause extensive platter damage or debris which would have been caught by the filter to the top right of the image. This particular case most likely points to this drive having an abrupt power failure / disconnect and the heads were returning to the parking ramp as the drive was spinning down.