Tennis elbow is soreness or pain on the outer part of your elbow. It happens when you damage the tendons that connect the muscles of your forearm to your elbow. The damage makes it painful to rotate your forearm and flex your wrist and fingers backward.
The cause is usually overuse from repeated hand and wrist movements. These movements are sometimes a part of everyday activities, like using a screwdriver. Or the overuse can come from playing sports, like tennis.