The science of biomechanics, especially motion analysis, has been applied to sports for improving performance and preventing injury. Motion analysis is the foundation for further biomechanic analysis to better understand the injury mechanisms in sports. The goal of this article is to familiarize the reader with the basic biomechanics and motion analysis knowledge applied to sports and to improve physicians’ understanding of sport injury mechanisms. Applications of biomechanics and motion analysis to baseball pitching are discussed as examples.