My dad and I have long talked about how it seems odd that there isn't a stat that breaks down how well hitters do depending on who they are facing. Of course, we expect that MOST hitters will excel against Brad Penny-caliber pitchers and do poorly against the top-echelon pitchers, but I think there is a bigger gap in some hitters than in others.
My argument is that batting stats should always be taken with a grain of salt because certain hitters beef up on their stats by destroying bottom-tier pitchers (let's define those as pitchers in the bottom 25% in ERA... or wait, let's be geeky and make it FIP)... but don't have any success against top-tier pitching (defined as pitchers in the top 25% in FIP).
Now, I don't have any statistics to break this down (could someone possibly work the magic stat-computing-machine to generate something?), but the question of "How well can you hit pitchers who are at their best?" seems like an intriguing one to examine... especially in anticipation of facing "playoff pitching."
For example (assuming the Tigers do play the Yankees), my assumption (from observation) would be that hitters like Granderson and A-Rod get more-or-less owned by the best pitchers (then feast on the worst pitchers -- particularly throughout A-Rod's career), whereas players such as Jeter (even if he's not having a great season this year) or Cano (who is) have the ability to match-up against the best pitchers and find success.
On the Tigers' side of the coin, my guess would be that players such as Austin Jackson or Brandon Inge have done miserably against the best pitchers over the course of their careers (how many of Brandon's 27 HRs came off of good pitchers in '09?). However, I think that players such as Cabrera, Martinez, Avila and Delmon can hit ANYBODY. As for others? I'm not sure. All this said, of course one expects a dip in success when you're batting against the best... but we need a gauge to measure HOW MUCH that dip is... Isn't this a differential that is worth exploring?
Why have I not heard this come up before? Is there an existing measure of this that has been buried and is horded by stat nerds but not expressed in any mainstream baseball analysis? Doesn't it seem like there some players who will have more or less than same level of success no matter who they're facing (i.e. Vladimir Guerrero or Polanco or Damon or Ichiro)? And, by the same token, players that have misleading/padded stats because they are wreaking havoc the poor #4 & #5 starting pitchers of the world?
Would love to hear people's comments. I'll stop my rant now :)