[Performify]

In theory, a book would love balanced action (50-50 on each side) but in practice it doesn't happen.

Ultimately, it really doesn't matter. With Vegas lines of -110 or worse, a very high percentage of people can't overcome the juice long term to win, regardless of balanced action. So while a Vegas sports book may in theory experience revenue swings when a large public favorite covers one weekend, they're going to be a long term winner every time simply because of that rip they're taking from every bettor. In short, just like Party, they don't have to rig things: they're taking a rip from every pot, they just want to see a lot of volume.

What you talk about, with a book taking a position on a game, that's certainly a part of it. Linesmakers know a certainly amount of people are going to bet on Notre Dame, or Indy, regardless of where they set the line, for example. So that fact gets factored in to the line that's ultimately set... but in general these days, books can't risk hanging a rouge line by taking an extreme position on a game, because they'll get slammed from "scalpers" - people hammering at that rouge line and offsetting the action elsewhere to lock in a guranteed profit.

This is covered in brief in the FAQ in the question "how do the books make money?". I'll take a look at expanding that answer...