When we talk about "background information" for research, we're not talking about the history of your topic.  We're talking about the first stage of your research.  Before you dive into articles and books, it's a good idea to have an overview of your topic.  This can help you discover what interests you most about it and what you would be most excited about researching.  That way, you can narrow your book and article searches to the items most relevant to your interests.  Reference sources (encyclopedias, primarily) are filtered both in terms of quantity and in terms of quality, so they're concise and trustworthy - an excellent place to go to get that overview.  This page has tools for finding encyclopedias that may work for your Olympic topics.