In an effort to provide the best and most complete baseball coverage possible, there's been an increase in the use of analytics and advanced metrics on these pages in recent years.
While the general rule is that every stat should be able to be explained in one sentence within those stories, here's a rundown of some of the most frequently used ones to reference as the season goes on.
WAR (wins above replacement) — One of the more ubiquitous stats in the game, this tries to approximate a player's value over a minor leaguer who would take his place in the event of an injury. While it can be used for both position players and pitchers, the metric is more useful for position players, as it combines offensive and defensive value in the league's context to capture the player's value in the amount of wins that player accounts for.
OBP, SLG and OPS (on-base percentage, slugging percentage and on-base-plus-slugging) — These are the three most basic stats on this list with OBP and SLG being the last two items seen in our most commonly used hitting stats, the slash line. A slash line appears in stories as, batting average/OBP/SLG (.300/.333/.490, for example), with the latter two numbers being added together to form OPS, accounting for how often a batter reaches base and how many extra-base hits he is accounting for. These numbers go beyond batting average to illustrate how much offense a hitter contributes.
wOBA (weighted on-base average) — In an effort to paint a more full picture of offensive performance, this statistic weighs each individual outcome at the plate (from a single to a home run) differently. Unlike OPS, which weighs the on-base and slugging portions of that combination equally, wOBA attempts for a more complete offensive picture while still valuing each component fairly.
wRC+ (weighted runs created plus) — Like wOBA before it, this measure uses the specific value of each offensive event, puts it in context with that year's overall offensive scoring environment and ballpark factors to place it on a scale where 100 is league average each year.
UZR (ultimate zone rating) — One of the premier defensive metrics, this takes into account range, arm strength, errors and double plays to measure a player's defensive worth in runs for or against his team. It gives each batted ball an expected value based on how many runs it could be worth, then adds it to or subtracts it from a player's account based on whether he converts it into an out. This is most commonly presented as UZR/150, which averages out a player's UZR at a position over 150 games to make it easier to compare with others.
DRS (defensive runs saved) — Like UZR, this measurement tries to replace fielding percentage and errors with a more complete defensive picture. It uses the expected run value of batted balls — depending on whether a defender converts it into an out or not — to show a player's defensive value to his team.
FIP (fielding independent pitching) — A pitcher's earned run average (ERA) is often used to paint a picture of his overall performance, but so many things beyond the pitcher’s control — namely defense — are a factor. FIP takes the three factors that a pitcher can control — walks and hit by pitches, strikeouts, and home runs — and uses a standardized figure for batted-ball luck and sequencing to replicate an ERA.
xFIP (expected fielding independent pitching) — A subset of FIP, this substitutes a pitcher's actual home run-fly ball rate with the league average of around 10 percent to erase any kinds of large variations that might arise in a home run rate in a given year.
WHIP (walks and hits per innings pitched) — Since this is on the front page of Major League Baseball’s stats, it doesn’t need to be explained too deeply, but with four letters in its acronym, here we are. This is an average of how many runners a pitcher allows to reach base per inning, with the lower the better. Base runners can create dangerous situations, so pitchers want to limit them.
ERA — While often compared by their ERAs, pitchers face different circumstances in the ballparks they pitch in and the competition they face. ERA- (and FIP- and xFIP-) use the corresponding park factors and league ERA to normalize some of those factors, with league average set to be around 100.