He used the metaphor of a plow horse to describe hockey player Ray Bourque. Read the sports section of a newspaper for a couple of days. Even the names chosen by sports teams can be seen as metaphors. For example, the team members of the Panthers want to be seen as large, wild cats known for their stealth and strength. Read this list of sports team nicknames for inspiration.
Violent metaphors appear in more places than just sportswriting.
Think of everyday language. Sometimes we use metaphors in an attempt to explain a situation that we are confronting in our daily life. Writers aren't the only ones who rely on metaphors to describe objects and events. Historians and scientists use them, too. There are other themes that inspire sportswriters, such as tales of fellowship or leadership.