Good question. The subject matter would be related to sports. One section would be about Soccer, one about Football, one about Basketball, and other sports to come soon. Each section would use a slightly different theme to give it it’s own look so to the user it would visually seem like a different section.
Each section / sport would have their own keywords they target related to that sport.
The reason for having one WP instal is to easily manage the site and allow users to be logged in between sections, and to programmatically share data across different section. For simplicity I would rather have this on one WP install.