Welcome to WebmasterWorld, Rosyanne. Check the Community Building Library [webmasterworld.com] for some ideas on how to grow traffic when you are first starting out.
Be aware that monetizing a forum IS difficult, but before you think about monetizing it you'll have to get volume to a fairly high level. Whether you are running CPM ads, CPC ads, or affiliate links, your revenue will depend on unique visitors and pageviews (along with other factors). Sports forums probably offer some good opportunities for promoting tickets, fan merchandise, etc. Good luck!