Most of us are guilty of assuming a lot when we write an article for Pinstripe Alley. Since I joined here in 2009 sabermetrics have reigned supreme, which required a bit of learning for someone who had never really tried to analyze baseball before. There are a lot of acronyms that get thrown around in articles on the site that may not be immediately obvious to people who are just finding themselves learning about sabermetrics, advanced stats, baseball, whatever. Sure, we could just say to Google it, but I figured having a resource on the site to point to when people were confused may be more helpful after a few requests lately. So here we are. Feel free to add any you may think of in the comments below.
BABIP: Batting Average on Balls In Play
Around 30% of batted balls fall in for hits. This can be used for pitchers or hitters to determine whether Lady Luck is being kind or cruel to a player. Sometimes a ball is hit right on the nose but right at a well-placed defender. Sometimes a ball is blooped into no man's land and looks like a line drive in the box score. Sometimes a ball is hit three steps to the left of a 40-year-old shortstop and goes for a hit when at least 20 other shortstops would likely be able to make the play. BABIP helps sort all that out.
DRS: Defensive Runs Saved
A metric that shows how above or below average a player is at saving runs defensively. No one defensive metric is going to paint a perfect picture, if you believe in defensive metrics at all. Fangraphs claims you need three years of defensive data and a combination of different metrics like DRS and UZR (Ultimate Zone Rating) to draw real conclusions.
FIP: Fielding Independent Pitching
An idealistic statistic of what a pitcher's ERA should have been. FIP can be used to determine that a pitcher is due for regression one way or another if they are getting particularly lucky/unlucky.
GO/AO: Ground out/Air out
This one is used frequently in the minors recap to show what kind of results a pitcher got. How many ground ball outs (GO) did they get vs. outs via the air (AO).
WAR: Wins Above Replacement
This is going to be the big one, and there are two different kinds. Fangraphs WAR (fWAR) and Baseball-Reference WAR (rWAR) differ slightly in their calculation, but it's nice to see how each grades out a player and how closely they agree. Basically the goal is to figure out how much more valuable Player X is than an average replacement. Mike Trout is a superstar, so the Angels would lose a lot replacing him with some kid from their Triple-A team. If Francisco Cervelli got hurt the Yankees could basically replace him with John Ryan Murphy and not be much worse off, if at all.
WHIP: Walks + Hits per Innings Pitched
Self explanatory, right? How many people is Pitcher X putting on base?
wOBA: Weighted On Base Average
Here is Fangraphs' explanation of wOBA:
wOBA is based on a simple concept: Not all hits are created equal. Batting average assumes that they are. On-base percentage does too, but does one better by including other ways of reaching base. Slugging percentage weights hits, but not accurately (Is a double worth twice as much as a single? In short, no). On-base plus slugging (OPS) does attempt to combine the different aspects of hitting into one metric, but it assumes that one percentage point of SLG is the same as that of OBP. In reality, a handy estimate is that OBP is around twice as valuable than SLG (the exact ratio is x1.8).
Weighted On-Base Average combines all the different aspects of hitting into one metric, weighting each of them in proportion to their actual run value. While batting average, on-base percentage, and slugging percentage fall short in accuracy and scope, wOBA measures and captures offensive value more accurately and comprehensively.
WPA: Win Probability Added
Measuring outcomes on a play-by-play basis. A home run in the bottom of the ninth in a tie game will swing WPA much more than a double in fifth inning of a six-run game. WPA adds context to the outcomes to determine how much they helped or hurt the team's win expectancy.
wRC+: Weighted Runs Created Plus
This statistic is often used in our analysis here to discuss the offensive output of a player. How good is Player X at creating runs compared to the league? The plus on the end means that it has been league-adjusted. Anything under 100 means below league average and anything above 100 means above league average. A 110 wRC+ is 10% better than league average, and so on.
If you have any others you'd like to see added, feel free to ask in the comments below.