A little over a year ago I wrote the first DRB Stats Guide which has its fair share of mileage. So today I offer a new one in a different format.
What stats should I use to evaluate pitching?
On a game to game basis:
- Home runs (to a lesser extent, explained below)
- Ground balls
- Swinging strikes
Those numbers play into FIP (which is like ERA, only it strips the defensive aspect from the equation) and xFIP (which is FIP, which strips the home run luck aspect from the equation) as well as tRA. Those are the three quick references for allowed run estimators. Home runs are tricky because research has found that most pitchers will regress towards ~11% home runs on all fly balls given up. That means, a number that far exceeds (or undercuts) 11% is probably a combination of luck and/or environment more so than skill.
You can find the majority of those stats at any ol' place (like Baseball-Reference) but FanGraphs features batted ball data as well as plate disciple data, which includes Contact% and handy averages.
I highly recommend reading Dave Cameron's guide to evaluating pitchers. It's dated, but still good.
What stats should I use to evaluate hitting?
If you hate using wOBA, then:
Otherwise, just use wOBA. It correlates closely with runs scored and weighs the value of OBP better than OPS does (one point of OBP is worth 1.8 of SLG).
What stats should I use to evaluate fielding?
What stats should I avoid using as measure of value?
What are appropriate sample sizes for single season numbers?
These come from a Pizza Cutter post that went lights out when MVN did, but the figures represent the place where R = .5:
50 PA - swing percentage
100 PA - contact rate, response bias (both just missed at 50... the real number is probably around 70)
150 PA - K rate, line drive rate, pitches/PA
200 PA - BB rate, grounder rate, GB/FB ratio
250 PA - flyball rate
300 PA - HR rate, HR/FB
350 PA - sensitivity
400 PA - none
450 PA -none
500 PA - OBP, SLG, OPS, 1B rate, popup rate
550 PA - ISO
600 PA - none
650 PA - none
How can I do quick projections?
1. Take the last three years of data, and weigh it on a 5/4/3 scale.
2. Add a "2" that represents league average.
3. Average this out.
4. Adjust for park, league, age, etc.
Or just find the newest ZiPS or CHONE projections.
Is scouting still relevant?
Yes. It's another piece of information, just like numbers.
For mostly every other stat's definition and usage, I'd direct you to FanGraphs glossary and this.
Hopefully this is streamlined enough so that people who need primers and refreshers actually use it.