Yahoo! has always done a pretty good job generating pageviews and interaction from sporting events and box scores.  Specifically, their industry leading fantasy sports tools are top notch have about 40% marketshare among the 27M Americans who participate fantasy sports.

With the release of the iPhone app, Yahoo! Sportacular, the company is layering on more social features onto sports box scores and game announcements.

Check out this screen shot from the service.

You can now check-in to games (watching on TV or attending), pick winners, and trasht… err, chat with other fans (using your Facebook login).

Upon check-in, you get access to a map overlay of check-ins by each team’s fan base, as well as a quick glimpse of which team’s fans are checking in more.

Yahoo! isn’t the first company to do sporting event check-ins. has an app, cleverly hidden behind a $6.99 price tag, that lets fans checkin to games.  And Fanvibe is a startup focused on social sports related checkins.

But Yahoo! has a massive, built in audience for sports box scores.

Sportacular should appeal to quite a few of those people.