[mcrowder]

If work football as well, and know from whence I speak when I say that it's a completely different animal.

In football, you have an area of responsibility and are responsible for everything that happens in that area. There is a LITTLE bit of overlap (holding in the interior, sometimes illegal man downfield, interference in the gaps, etc), but most calls belong to one guy.

In baseball/softball, it's not as cut and dried. There are some calls that "belong" to one umpire, and some that don't. OBS and INT fall into the "don't" category. I doubt it's mentioned in a book, but it is definitely discussed in clinics, especially on-field clinics.

And there's a reason for it. BU has multiple responsibilities and will NEVER be able to constantly watch a runner, or he fails in his other responsibilities (especially with multiple runners). PU has to get into a position as well, but is nearly always facing the field, and has more of a full view of the possible OBS/INT's.