A mallet finger, sometimes called “baseball finger” because it can be common in baseball players, is a deformity of the finger typically caused by injury. You may have a mallet finger if you’ve recently jammed, cut, or broken your fingertip. Most likely, a hard object like a ball struck the tip of your finger or your finger was bent forcefully when lifting a heavy object or performing a daily task.
Source: Handcare (ASSH)