Batting average, runs batted in, runsscore, pitching wins, and earned run average are some of the statistics thatcome into the mind of even the most casual baseball fan.

Generations of casualfans and team front offices in baseball have used traditional statistics. Thatchanged when Bill James and the pioneers of sabermetrics knew baseball neededto be looked at through a new lens. This presentation will break downsabermetrics into three main categories, describe the most important metricswithin those categories, and explain wins above replacement.Sabermetrics was created for baseball fansto learn about the sport through objective evidence. This is accomplished by evaluatingthe performance of players in every aspect of the game. Every sabermetric wascreated by finding a flaw in a traditional statistic, or even by finding theflaw in another sabermetric. The three overarching categories are batting,pitching, and fielding also known as defense.The traditional measure of batting performancewas considered to be batting average.

This is calculated by taking the numberof base hits divided by the total number of at-bats. The fathers ofsabermetrics found this measure to be flawed as it ignores the other ways a battermay reach base. This led to the on base percentage (OBP), which is calculatedby the total number of hits added to bases on balls along with hit by pitch,and divided by plate appearances. The second flaw with batting average is thatit does not take into consideration doubles, triples and homeruns, and givesall hits the same value which is known to be untrue.

This is where the creationof slugging percentage comes from. When these two statistics are combined, theycreate on base plus slugging, OPS. OPS has become useful in comparing playersand is an accurate method of predicting runs scored from a certain player butis still missing context. This is where OPS+ comes into play. OPS+ takes ahitter’s OPS and adjusts for the league average OBP, slugging percentage, andthe hitter’s home ballpark. This puts everything on a scale of 100, with anythingabove 100 being above average and below 100 is below average. This allows fansand front offices alike to have a quick objective comparison to these player’svalues and can even be used to compare players in different years.

The second category players are evaluatedon is pitching. Traditionally pitching performance was based on the pitcher’s earnedrun average (ERA). This is calculated by dividing the number of earned runsallowed by the pitcher by the number of innings pitched and multiplying by nine.ERA is largely flawed as it is affected by things outside of the pitcher’scontrol such as the quality of his defense. This is where field independent pitching(FIP), c, and skill interactive ERA (SIERA) come into play.

Field independent pitching (FIP) is theeasiest to understand of the three stats. It focuses on the four controllableoutcomes: strikeouts, walks, hit by pitch, and homeruns. The largest complaint aboutFIP is that most people don’t agree that pitchers can control homeruns. This iswhy expected field independent pitching (xFIP) was created. This stat replacesthe pitcher’s homerun total with an estimate for how many homers he should haveallowed.

That is calculated by multiplying the league-average homerun to flyball rate by the pitcher’s fly-ball rate. The next complaint is that pitchers shouldhave control over batted balls and need to be rewarded for ground balls. This iswhere skill interactive ERA (SIERA) is important.

Skill interactive ERA (SIERA) focuses onthe same things as FIP and xFIP, except it calculates for batted balls. NamelySIERA is able to recognize how run prevention improves for a pitcher the moreground balls they induce as they lead to fewer base hits, easily become outsand get double plays. When it comes to SIERA ground ball percentage is the key. Now that we can determine the value ofa pitcher without accounting for their defense the only thing left to do iscompare pitchers from other leagues and ball parks.

This is done with ERA+.ERA+ has the same affect as OPS+ as it puts the players on a relative scale to eachother with league average at 100. A great case study for this is looking atClayton Kershaw’s 2013 season versus Pedro Martinez’s 2000 season. Both playershad the best ERA in their respective leagues for those years.

Martinez had a1.74 ERA while Kershaw had a 1.83 ERA. At a glance these numbers would seem to showthat they were nearly equal except the difference in ERA+ is astounding.

While thedifference was only .09 ERA, their ERA+ was Kershaw 196 while Martinez was 291.This perspective makes Kershaw’s season seem like child’s play. The keydifferences between the two was that Pedro Martinez put up his numbers in the middleof the homerun heavy steroid era while Kershaw’s season was a pitcher friendlyone. This should give some context into how different of a lens sabermetrics providesus.The final category of sabermetrics isfielding.

At this time the baseball community has not agreed on how to measure thedefense metric. Baseball-Reference.com uses defensive runs saved (DRS), while FanGraphsuses ultimate zone rating (UZR). Both of these stats attempt to calculate thesame thing, how many runs above or below average a player is on defense. With twodifferent systems being in place this leads for two potential differentoutcomes when attempting to determine a player’s defensive value. This complicatesthings when attempting to determine a players WAR (wins above replacement). The final sabermetric is wins abovereplacement (WAR), used to evaluate a player’s contributions to his team.

WARcompares a certain player to a replacement-level player in order to determinethe number of additional wins the player has provided to his team. WAR values varywith hitting positions and are largely determined by a player’s successfulperformance and their amount of playing time. Considered a catch all statistic thatcarries heavy weight from everything to how much a player is worth monetarilyto Hall of Fame considerations. When determining the WAR of apitcher, the main factors are innings pitched and runs allowed.

Baseball-refrence.comlooks at total runs allowed, while FanGraphs uses FIP as their base. This meansthat FanGraphs WAR (fWAR) is more hypothetical while Baseball-Reference, ismore about actual value. While determining WAR for pitchersis simple and effective, determining WAR for position players can be a bit murkier.WAR should be the ideal way to determine the value of position players as itincludes how many runs hitters produce with batting and baserunning along withhow many they take away with their defense.

While hitting and baserunning are agreedupon by Baseball-Reference and FanGraphs, as stated earlier defensive metricsare not. Sometimes their systems provide similar results, and other times they arecompletely different. This does not invalidate WAR by any means, but you mustbe careful with what source you want to use when discussing players by their WARs. Sabermetrics are used for multiplepurposes, but the most common are evaluating past performance and predicting futureperformance to determine a player’s contribution to the team. These statistics areused from everything to determining Hall of Fame votes, end of the seasonawards, and relative value when teams make trades or offer contracts to freeagents.

Sabermetrics can even be adjusted for minor leaguers allowing the big-leagueclubs to make better decisions regarding their prospects in the farm systems.