If you are referring to the Top 10 on home page, they are ranked by averages. But like I mentioned, everybody is playing so scores are constantly changing every minute. The actual rankings aren't updated until later though. So you'll see someone who was ranked #5 with a 69.0 avg the instant the list was compiled (let's say midnight) who plays 2 bad rounds and now their 69.0 avg changes to 70.0 (I'm using arbitrary numbers here).
Since rankings aren't updated until the next midnight, even though 70.0 is no longer a top 10 average, you're still ranked by the 69.0 you had when the stats were compiled at midnight.
Perhaps I'm mis-understanding what you're asking. Does that help clear it up any better?