Lately when I backwash my above ground pool, the filter blows out sand into the water. What causes this? When backwashing the filter, I turn off the pump, turn the dial to backwash and turn the pump on low. Is the pump supposed to be on during the backwash and rinse cycle?

Your filter media is the sand but there are screens that hold the sand in place. A screen may have a tear in it.

Need more clarification. What can be done to fix the problem?

If there is a chance the screen is torn you must disassemble the filter housing and pull out the screens. Inspect each screen and seal carefully and buy replacements as needed.