Originally Posted by Mario-Rijo
I've got a question on the main topic Cyclone. What if anything does this do to quell the myth a bit that hitters don't improve their plate discipline much (if at all) over the years?
Short answer: it's a myth for good, young hitters who show decent plate discipline skills at an early age (minor league career and early big league career). But it's mostly accurate for hitters who were hacks at an early age (minor league career and early big league career).
Now the long answer ...
The average hitter will possess his greatest plate discipline skills in his early to mid 30s while all his other skills decline. So if one went strictly by that notion, then the myth appears to be nothing more than a myth. However, it is also important to remember that most poor hitters - most of whom also have lousy plate discipline - fall out of the major leagues prior to reaching their early to mid 30s so those hitters are no longer applicable.
Now what I've typically found is that good, young hitters who show a propensity at an early age for plate discipline can in fact improve their plate discipline as they progress into the majors up into their peak years and beyond (up to early to mid 30s).
The cutoff I've noticed tends to be around a 12 PA/BB ratio in the minors, hence rule one. This isn't a hard cutoff by any means, but it's around that number where we tend to see guys go one way or the other. If a hitter's PA/BB ratio is on the good side of 12 PA/BB, then his chances are pretty good to see some further plate discipline improvement. If he's sitting down around 16 PA/BB, for example, then his chances are pretty lousy to see any plate discipline improvement and the vast majority of those hitters end up being lifelong hacks.
Rule two expands on this by showing us how a hitter progresses in his first three or four big league seasons. If you have a hitter who posted a 12 PA/BB ratio in the minors, you want to see improvement to a 10 PA/BB ratio within 1,500 to 2,000 PAs (prior to peak years) in the majors. If you have a hitter who posted excellent PA/BB ratios in the minors, such as a Votto or a Dickerson, you want to see his big league PA/BB ratio fall no worse than 10 PA/BB within 1,500 to 2,000 PAs in the majors.
What this means it that a guy such as Encarnacion - who achieved rule one - has always been a pretty decent bet to improve his big league plate discipline. And in 2008, that bet has turned up some winnings as he's now achieved rule two. Moving forward, that Encarnacion bet is likely to turn up even more winnings. He could very well be a guy who could reach 70+ walks in his peak years, and then we'd be talking about some serious on-base percentage.
It also means guys such as Brandon Phillips and Wily Mo Pena, for example, have been lousy bets to improve their big league plate discipline. They're both hacks, and they're both likely to be hacks throughout the duration of their respective careers. You'll be sniffing long and hard to turn up some winnings on those types of hitters.
This is important because plate discipline - and IsoD - can provide us with a lot of valuable information about what type of power a hitter may develop. When IsoD and plate discipline improves, slugging and IsoP improves. If IsoD remains flat and poor, then slugging has a very low cap. We don't see hitters post .320 on-base percentages mixed with .520 slugging percentages. Those hitters typically do not exist, and if one does pop up, he's a rare breed.