TAC SCM is a supply chain management game for the Trading Agent Competition (TAC). The purpose of TAC is to spur high quality research into realistic trading agent problems. We discuss TAC and TAC SCM: game and competition design, scientific impact, and lessons learnt. With a conscious effort to these ends, a competition may help focus research on well-chosen problems in high impact domains, facilitate comparison of results, and create a community eager to analyze and build on the results of peers and in working jointly towards the perfection of solutions. Potential pitfalls include emphasizing winning to the exclusion of testing scientific hypotheses, and carrying the overhead of designing, implementing, and operating a competition.