Mallet finger is a deformity which bears resemblance to a mallet. When the distal interphalangeal joint is forced into sudden hyperflexion due to an impact, the severe tension on the long extensor tendon tears away part of its attachment to the phalanx. As a result, the person cannot extend the dital interphalangeal joint. This type of injury is common in baseball players when the when the baseball is miscaught and forces the DIP into extreme flexion. Hence, tearing the extension tendon. Images via: https://images.app.goo.gl/2p5FtPS8Ks8ZUe246 https://images.app.goo.gl/m7grxu85tEpm1M1a9