I've been worshiping at the sabermetric altar for as long as I've been aware of Sabermetrics, and so OPS (On Base Plus Slugging) and OPS+ (OPS adjusted for park and league) have been my guiding offensive lights for years now, although as I mentioned in my ALCS preview, I've recently been moving away from OPS and looking more at wOBA (Weighted On Base Average) as a guideline, as it's a better tool for calculating overall offensive performance.
On the pitching side of things, I like ERA+, as, like OPS+, it is adjusted for park and league. However, I've begun to move away from ERA+ and have been growing fonder of FIP (Fielding Independent Pitching), although we'll get to that shortly.
For both OPS+ and ERA+, 100 is league average. For hitters, 140+ and higher is generally considered elite (to wit, the top ten OPS+ finishers in 2009 range from the absurd -- Albert Pujols at 188 -- to the slightly more benign -- Ben Zobrist at 144), while on the pitching side, the top guys are generally putting up a 130+ and higher. If you're still somewhat confused about OPS+ and ERA+ and the above links haven't helped, here's another helpful explanation of the two statistics.
Moving on to my new favorites, we have Weighted On Base Average, or wOBA. I'm going to re-post what I wrote in the ALCS preview post:
"I've been a huge OPS proponent for as long as I've been aware of the statistic, but as many have recently pointed out, OPS is not the be-all end-all measure of offensive prowess that a lot of folks (including myself) have made it out to be. Its primary flaw is that by combining OBP and SLG, it does not accurately reflect a player's true value, for you could have two players OPSing .800, with one posting an OBP of .400 and SLG of .400, and the other an OBP of .300 and a SLG of .500. Not that a SLG of .500 is bad, mind you, but a .300 OBP is pretty putrid, and most people would probably take the guy who's getting on base at a .400 clip.
As per FanGraphs, 'wOBA is a linear weight formula presented as a rate statistic scaled to On Base Percentage. Essentially, what that means is that average wOBA will always equal average OBP for any given year. If you know what the league’s OBP is, you know what the league’s wOBA is. Usually, league average falls in the .335 range – it was .332 last year, but offense was down around the game in 2008, which may or may not continue.
So, why should you care about wOBA? What makes it better than OPS or any of the more famous rate statistics that measure offensive value? The beauty of wOBA lies in linear weights. Essentially, every outcome has a specific run value that is proportional to other outcomes – a home run is worth a little more than twice as much a single, for instance. What wOBA does, as all linear weights formulas do, is value these outcomes relative to each other so that they are properly valued.'So there you have it. People way, way smarter than me have created a statistic that -- while not perfect -- seems to be the closest metric we have to the overall evaluation of a player's offensive contributions, independent of baserunners or how many outs there are.
To give you some additional context, A-Rod's 2009 OBP was .402, while his wOBA was .405, good for 10th-highest in all of baseball. So just in case you were worried (although at this point the ALDS really should have quelled any of your doubts), rest assured that A-Rod is still one of the best players in baseball."
As wOBA is scaled to On Base Percentage, all you really need to remember for wOBA is that .350 is decent, .370-.380 is very good and anything above .400 is phenomenal. If you're still unsure about wOBA, please check out FanGraphs' definition here.
On the pitching side of things, we have Fielding Independent Pitching, or FIP. FIP, as implied in its name, is a measure of everything that a pitcher is specifically responsible for independent of his defense, i.e. strikeouts, walks, home runs and hit by pitches. As Baseball Prospectus notes in the hyperlinked definition, FIP helps you understand how well a pitcher pitched, regardless of how well his fielders fielded. This is highly useful because, as we know, a wide variety of defensive factors can influence the outcome of a given at-bat that the pitcher doesn't have control over. FIP is probably the closest thing we have that accurately reflects a pitcher's ability to pitch.
For defense, we like Ultimate Zone Rating, or UZR, defined as the number of runs above or below average a fielder is in both range runs, outfield arm runs, double play runs and error runs combined. UZR/150 (ultimate zone rate per 150 games) -- the number of runs above or below average a fielder is, per 150 defensive games -- is also quite useful, and seems to have begun to overtake UZR as the defensive statistic du jour.
There are also a couple of statistics that attempt to capture a player's overall value. The two most frequently cited are Value Over Replacement Player (VORP) and Wins Above Replacement (WAR). As per BP, VORP is the number of runs contributed beyond what a replacement-level player at the same position would contribute if given the same percentage of team plate appearances. However, one drawback to VORP is that it does not consider the quality of a player's defense. Here's a more thorough definition of Replacement Level.
To give you some additional context for VORP, National League MVP Albert Pujols (98.3) and American League MVP Joe Mauer (91) had the top two VORP in baseball in 2009 for position players. Nice when that works, out, eh? AL Cy Young Zack Greinke (88.3) and Felix Hernandez (75.1) led all pitchers in VORP.
WAR essentially converts run values to wins -- for a far more comprehensive explanation of WAR and run and win values, please refer to FanGraphs. Ben Zobrist actually had the top WAR in baseball in 2009 (8.6), besting both Pujols (8.4), and Mauer (8.2).
So again, when discussing offense, you'll primarily see me citing wOBA, OPS, OPS+; and when talking about pitching, I generally use FIP and ERA+. For overall value we use VORP and WAR, as well as FanGraphs' Dollar Value.
That isn't to say you won't see other advanced statistics cited here from time to time (Isolated Power, or ISO, comes to mind), and if I discuss something I may not have mentioned previously, I'll do my best to define it.