Is it legal to create a website for tournaments?

Contact the game company and tell them what you want to do. You cannot do it without their written permission because you would be using the name of their fame, their trademarks, and possibly their character photos, on which they own the trademark and copyright. The company might very well say yes if you present yourself in a professional, organized manner. If you run the tournament without their permission, you risk they will send you a Cease and Desist letter and wreck all your fun midstream. On the other hand, if they like you and what you plan to do, the tournament could be good publicity for their game. Go ahead and contact the company. You won't know till you try.