It wouldn't be for MMA. It's for everything: festivals, fairs, races, games...
Oh, then it really depends on the sophistication of your database and if you intend to have any e-commerce involved. If not you really just have to decide how you gather and display the info.
Complexity all really depends on how much security you need overall and the degrees of it. If you're just serving info it's not terribly hard just writing mainly scripts to retrieved the data based on your form searches and featured events etc. To gather the data you can either scrape other sites for it (requires more work at first and can get complex but is much more adaptable later) or create a system of submissions (needs a community or incentive for the continued content and involvement) or do the work yourself (not likely in the long run but you can at first as it is incredibly time consuming as you expand the types of events you want to track).
My answer is more vague than people who have actual experience in writing them would give, I know the jist of what is entailed but I have never written a full app, Splinty may have and in this site's function he is part of, is guaranteed to have more experience than I do right now.
