Best Starting Pitching Metrics and Measures of MLB success

I look to WHIP. The down side of this measure is it does not factor in what the hit was, a single and a homer counts the same. Maybe if slugging % against were added to WHIP for a similar measure to OPS.That measure may exist somewhere but I have yet to find it.

Good thread topic. I personally don't like the idea of looking for a magic bullet solution among stats; they each tell something different, and I'm personally not comfortable enough with any all-in-one solution (WAR being the obvious example) to use them exclusively. To me there is still some "art" left among the science of advanced stats, and that's figuring out which ones to apply and when. FIP vs. xFIP is an example (and yes, some people will completely ignore both, which is fine too) - From the MLB.com advanced stats glossary So, at a high level, xFIP acknowledges that there is such a thing as a groundball or flyball pitcher, but not a pitcher who is any more "homerun prone" than their flyball rate would suggest. On *average* xFIP should be more accurate, or at least that was the case a few years ago, but there are (I believe) absolutely some pitchers who have a skill at limiting homeruns - a version of the whole "ability to limit hard contact" debate. To me, that means that xFIP may be worth looking at, but not in a vacuum.

I know this isn't what you want to hear, but you're probably best off doing some research and finding out what mix of stats you think are worth looking at, and then looking at all of those if you're really trying to evaluate a pitcher's performance. For a high level understanding of some of the more advanced stats, I actually think the MLB.com glossary does a pretty good job of explaining them: www.mlb.com/glossary/advanced-stats - they're each a very quick read.

As far as stats you didn't mention, I think wOBA and xwOBA allowed are very much worth looking at for pitchers - they aren't always going to be perfect, but try to determine the impact of every plate appearance on scoring runs. wOBA will try to tell you what happened, xwOBA will try to tell you what should have happened. The incorporation of statcast data into the expected outcome is something I find particularly interesting, although also not perfect.

One other thing that I think gets lost sometimes in this conversation: with enough of a sample size and/or a long enough trend, almost any stat starts to be meaningful. ERA may not be anywhere near as predictive as some other numbers, but if you have a pitcher who's put up an ERA of 3 in a full season each year for the last 5 years, then all things being equal, its a pretty good bet he'll put up an ERA around 3 next year, too. The "all things being equal" piece is critical though, and again, you likely need some of these more advanced stats to spot if things really are still "equal" or not. Because of this, evaluating prospects through statistics is - as far as I'm concerned - really challenging at best, as so many things change so frequently as players progress through the minors (which is also why this site is so much fun.) In those cases, the smaller component stats, K%, BB%, things like that, may be at least a little bit safer, but still need to be considered with a ton of context.

Speier did an AMA a couple weeks ago and said he thought Baseball Prospectus had the best group of stats. I think he said theirs were the closest to how he understands front offices evaluate players.