Knee cracked hard now i have stinging below the knee cap and leg cramps?

Many thoughts: You may have had the patella slip sideways or may have had a piece of cartilage get caught between the upper and lower leg bones. If there is no swelling, heat or redness, one may wish to ice the knee, take some Ibuprofen type medications for pain and rest the joint as much as possible for a few days. If this doesn't work, get seen by pcp or ortho doc.