A 19-year-old female collegiate rower presented with a new, painful mass along her right anterolateral chest wall after competition. The patient was diagnosed with a rupture of the serratus anterior muscle from its costal attachments, as confirmed by magnetic resonance imaging. The patient fully recovered after a period of rest followed by a graduated 2-month physical therapy regimen consisting of stretching and scapulothoracic and core strengthening. A traumatic rupture of the serratus anterior muscle should be suspected in athletes who present with a painful chest wall mass after exertion of large forces through the scapulothoracic region. Athletes can return to play after nonoperative management.