Isolated avulsion fracture of the extensor carpi radialis longus (ECRL) tendon is a rare and poorly understood injury. We present a unique case of a 45-year-old male who fell on his flexed right hand. He presented with a subtle but extremely painful mass on the dorsum of his wrist. Ultrasound (U/S) imaging of the mass revealed an avulsed bone fragment attached to the ECRL tendon, confirming the clinical suspicion of an ECRL avulsion injury. Computed tomography and magnetic resonance imaging are well-documented imaging modalities to detect tendon avulsions. As demonstrated by this case report, U/S is an excellent diagnostic tool for ECRL rupture, a cost-effective alternative that provides real-time dynamic examination of hand injuries. To our knowledge, this is the first case of ECRL avulsion diagnosed by U/S. The purpose of this case report is to educate the reader on detection and diagnosis of ECRL tendon avulsion using U/S, a time-efficient and cost-effective imaging modality that is infrequently used for this purpose.