Busch Stadium is the only stadium I've been to where there are sections numbered in the 500s yet the seats are down next to the field. That's something you would expect to see at quirky Wrigley Field in Chicago but it works.
503 is one of the many bleacher sections in the right field outfield, underneath the Coca-Cola patio and Homer's Landing which are private party areas for fans. You're not missing anything in those areas, I promise.
The bleachers aren't for everyone, especially people with bad or sore backs because there isn't much comfort and support. Don't expect the drunken circus here that you see in Chicago but it's still full of some of the liveliest Cardinals fans in the ballpark. The rows are a little on the small side and there are zero drink holders so make sure to hold your beer the entire time and to never sit it down because someone will knock it over.
Other gripes I have with the bleachers; you won't be able to see the scoreboards at all; they're directly above you and even when you turn around to look up, you can't really see the videos that well. Your back is also to the beautiful St. Louis skyline which serves as the backdrop of the ballpark, much like PNC Park, Comerica Park and Target Field.

The only reason people sit here is because the tickets are cheap and the view is a good one. So if you're not an uppity and picky Cardinals fan, have fun in 503 or any of the other bleacher seats. I know I love them!