Michael Munger of Duke University talks with EconTalk host Russ Roberts about the role of formal rules and informal rules in sports. Many sports restrain violence and retaliation through formal rules while in others, protective equipment is used to reduce injury. In all sports, codes of conduct emerge to deal with violence and unobserved violations of formal rules. Munger explores the interaction of these forces across different sports and how they relate to insights of Coase and Hayek.