What is the best them for a baseball blog?

Many themes do not have any SEO features built in. That said, Yoast is the most widely used plugin for SEO.

Personally, I think the “best” theme is a matter of opinion and my personal favorite is a premium theme. Themify.me Ultra. You can make purpose it for basically anything you want to do from a simple blog to a full on business website and even a nice storefront page for an e-commerce site.

Hope this helps!