Actually, I think the rank is how the players rank based on your leagues scoring system. In my non 5x5 baseball league, the ranks are different from my 5x5 league. For football IDPs, its all screwed up, with NFL bench players ranked ahead of Ray Lewis.
The O-rank does change during the year, at least for baseball. I think for baseball that its the three year averages method, so the current year is factored into that. Not sure about football though.
aka Bloody Nipples for baseball