David Ross is a nobody, comes to GABP and goes wild.
Arron Harrang's K/9 grew from the 4's to the 7's and wildly jumped into the 8's last year.
Then we see other players who go well for a few years then have a horrible year or two.
Beyond the obvious stuff like injury and ageing what causes these wild fluctuations? (I know there is always some variation from year to year, but I'm talking about significant changes).
Is there any value to the old "change of scenery" idea? Could it be a coach improving or messing up a player? Hard work? Luck?
How does one account for this from a statistical standpoint? EDIT: I threw in this last bit about accounting for this statistically, but a diiscussion of these variations was really what I was interested in.