Below are some of the terms I have and will be using.
Simply refer to this page, or the awesome library at FanGraphs in the future if you read an article containing a statistic you aren’t familiar with.
OPS and OPS+
Many have seen OPS, which is simply On-Base Plus Slugging Percentage. OPS has value as a metric because it is the only widely accepted statistic that accounts for all the different aspects of offense: contact, patience, and and power. You can find OPS on baseball cards and in game broadcasts, and it’s a simple statistic for regular baseball fans to understand.
OPS+ normalizes the statistic to the league average. A 100 OPS+ is league average, and each point up or down is one percentage point above or below league average. In other words, if a player had a 90 OPS+ last season, that means their OPS was 10% below league average. Also, since OPS+ adjusts for league and park effects, it’s possible to use OPS+ to compare players from different years and on different teams. Any statistic you see with a “+” sign, the same effect is carried to that.
Weighted On-Base Average (wOBA) is based on a simple concept: not all hits are created equal. Batting average would have you believe they are, but think about it: what’s more valuable, a single or a homerun? Batting average doesn’t account for this difference and slugging percentage doesn’t do so accurately (is a double worth twice as much as a single? In short, no). OPS does a good job of combining all the different aspects of hitting (hitting for average, hitting for power, having plate discipline) into one metric, but it weighs slugging percentage the same as on-base percentage, while on-base percentage is more valuable than slugging.
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.
wRC and wRC+
Weighted Runs Created (wRC) is an improved version of Bill James’ old Runs Created (RC) statistic, which attempted to quantify a player’s total offensive value and measure it by runs.
Similar to OPS+, Weighted Runs Created Plus (wRC+) measures how a player’s wRC compares with league average.
Batting Average on Balls In Play (BABIP) measures how many of a batter’s balls in play go for hits.
Isolated Power (ISO) is a measure of a hitter’s power. Or, to look at it another way, it measures how good a player is at hitting for extra bases.
Fielding Independent Pitching (FIP) measures what a player’s ERA should have looked like over a give time period, assuming that performance on balls in play and timing were league average. Pitchers have little control over balls in play, so a better way to assess a pitcher’s talent level is by looking at things a pitcher can control: strikeouts, walks, hit by pitches, and homeruns.
Obviously, a walk is not as hurtful as a homerun and a strikeout has less impact than both. FIP accounts for these differences, and presents results on the same scale as ERA. It has been proven to be much more effective than ERA at predicting future performance.
Wins Above Replacement (WAR) is an attempt by the sabermetric community to summarize a player’s total contributions to their team in one statistic. Its foundation lies within playing time, so typically the more innings a player accumulates, the more (or less) WAR a player will be credited with. In terms of dollars, one Win Above Replacement is worth around $5M on the free agent market.