Mallet finger is a condition that causes difficulty when straightening the end joint of a finger. Mallet finger although it is also known as “baseball finger”. This condition can be caused by a direct injury to the finger, such as when a ball hits the finger during sports or when the finger is caught in a door, or it can be the result of a degenerative condition such as osteoarthritis. As a result, you are not able to straighten the tip of your finger or thumb on your own. In some cases, a small piece of bone is pulled away along with the tendon. This is called an avulsion injury.The finger is usually painful, swollen, and bruised. The fingertip will droop noticeably and will straighten only if you push it up with your other hand. It occurs when the tendon that helps the finger straighten becomes damaged or torn, causing the end joint to droop or bend downward.