AVG – (Batting Average) A ratio of hits/at bats for a hitter. AVG assumes that all hits are equal, but we all know a home run is worth more than a single, so there are some issues here.
– (On-Base Percentage) A ratio of times on base vs. times at the plate. A more useful stat than AVG since it includes walks, but still assumes that walks and all hits are of equal value. OBP is emphasized in Moneyball.
SLG – (Slugging) Similar to AVG, but each type of hit gets a different weight. 1B = 1, 2B = 2, 3B = 3, HR = 4. This is a good measure of power, but these weights are not exact, a home run isn’t exactly twice as good as a double, in reality it is a bit less.
– (On-base Plus Slugging) A statistic that tries to paint the whole picture of batting by adding OBP and SLG together. While OPS is the best standard stat that is widely used, it still has issues as it assumes OBP and SLG have the same value. In reality, OBP is almost twice as important as SLG.
– (Weighted On Base Average) A statistic created by Tom Tango, that is used for a complete picture of hitting. It assigns a linear weight to each result of hitting (BB, HBP, 1B, 2B, 3B, HR) and gives it as a ratio to PA. It also removes intentional walks. The weights change from year to year but are usually fairly constant. wOBA is on the same scale as OBP, so it is easy to know what a good and bad wOBA is.
– (Weighted Runs Above Average) A measure of the amount of runs a player creates above or below league average. IT is calculated from wOBA and PA.
– (Weighted Runs Created) Similar to wRAA above, but is not a measure of runs above or below average, just the amount of runs created for the team.
– A statistic that measures the rate of wRC and compares to league average. It is the rate stat version of wRAA and wRC that also adjusts based on park factors. It uses 100 as league average. Above 100 is above average and below is below. It is in terms of percent above or below league average. For example Miguel Cabrera had a 192 wRC+ in 2013, meaning he was 92% better than league average. Similarly, J.P. Arencibia had a 57 wRC+ in 2013, meaning he was (100-57) 43% worse than league average.
– (Isolated Power) A stat that attempts to measure only the power of a hitter. It is the ratio of extra bases to AB. It can be calculated as SLG – AVG.
– (Earned Run Average) A measure of the amount of earned runs a pitcher would allow if the pitched 9 innings. ERA is the main pitching statistic used in baseball. It has the idea that the pitcher should not have to pay for his teams bad defence, so it eliminates runs caused by errors from the equation. If more knowledge of defence had been known at the time of creation, it would try to eliminate defence as much as possible. Since it doesn’t fully use defence, it is usually disregarded by sabermetricians.
– (Walks and Hits per Innings Pitched) Another widely used pitching stat that is used as a complement to ERA. It similar to OBP for pitchers as it measures how many walks an hits a pitcher gives up in an inning (3 outs).
– (Defence Independent Pitching Statistics) DIPS is not a statistic, but an ideology. It is the idea that a measure of pitching skill should not include the effect of the team’s defence. There are quite a few DIPS statistics, and I will go over the ones we use here.
– (Fielding Independent Pitching) The most commonly used and well known DIPS stat is based off of results that only the pitcher and batter can control. These are strikeouts, walks, and home runs. FIP is scaled to ERA so it is easy to tell what is good and bad. FIP is better at predicting future ERA than ERA.
– (Expected FIP) A version of FIP that uses the idea that home runs aren’t controllable by a pitcher, but fly balls are. It substitutes HR in FIP for the amount of HR a league average pitcher would give up with the pitchers amount of FB. xFIP is better at predicting future ERA than both FIP and ERA.
– (Skill Interactive ERA) A more complicated DIPS statistic that uses ground ball rates as well as strikeout and walk rates. SIERA is not linear and goes on a per batter basis, instead of per inning like FIP and xFIP. This per batter basis gives SIERA a predictive edge over ERA and FIP, and a slight edge over xFIP.
– (Truly Independent Pitching Skill) TIPS is another DIPS stat created by our own Chris Carruthers. It branches on the ideology that strikeouts and walks should not be used in DIPS since the catcher and umpire play parts in each. TIPS uses three stats that only the pitcher and batter can control that correlate well to ERA. These are O-Looking% (PitchF/x ratio of pitches outside the zone that are watched), SwStr% (percent of total pitches that are swung on and missed), and Foul% (percent of contacts that are fouled off). TIPS also scales to ERA. TIPS is on a per pitch basis, and this allows it to stabilize very fast. The fast stabilization gives it a great predictive edge over SIERA, xFIP, FIP, and ERA in samples that are less than IP. SIERA and xFIP pass it at 70 IP, while FIP passes it at around 200 IP.
ERA- and DIPS-
– These are stats that are calculated like wRC+, but for pitching. Each pitching stat can be put into XX- form with 100 as average. The “-” just indicates that a lower number is better (less than 100) while values above 100 are bad. This is to keep with the style of lower ERA being better. Park effects are accounted for.
– (Ultimate Base Running) This is a measure of the runs above average (like wRAA) that a player contributes with their legs, aside from stealing. UBR takes into account advancing on hits, flyballs, throws, grounders, etc. Some players are good at advancing even if they don’t steal (Colby Rasmus).
– (Weighted Stolen Bases) A measure of runs above average (like wRAA and UBR) that a player contributes from steal attempts. It uses SB and CS and weights them accordingly (about 0.25 runs for a SB and -0.5 for a CS).
BSR – (Baserunning Runs) A measure of total base running runs above average. Adds UBR and wSB together.
– (Speed score) A measure of the speed of a player. Uses real events to determine and is rate based, meaning it does not accumulate unlike BSR.
– (Ultimate Zone Rating) A relatively complicated stat that measures the runs above average at their position that a defender saves (contributes). For more complete information, click the link.
– (Defensive Runs Saved) Similar to UZR in that it measures the runs above average that a defender contributes. Each play and location on the field has an assigned run value determined from average players at that position. If the player makes a play that 75% of players miss, they get 0.75 plays to their DRS. If a player misses the play they would lose (1.00-.75) 0.25 plays. Plays are then converted to runs (usually just divided by 2).
GB% – (Groundball rate) The rate of balls in play that a hitter makes (or pitcher gives up) that are groundballs.
FB% – (Flyball rate) Same as GB%, but for flyballs.
LD% – (Line drive rate) Same as FB% and GB% but for linedrives. GB% + FB% + LD% should always equal 100%.
– (Homeruns per flyball) The ratio of homeruns hit (or given up for a pitcher) to flyballs. It is used as a luck indicator for pitchers and a power indicator for hitters. A high HR/FB% for pitchers may mean they are getting unlucky.
– (Batting Average on Balls In Play) Similar to AVG for a batter, but is the ratio of hits to balls in play. HR are not counted as hits or balls in play. It is the most widely used luck indicator for pitchers and batters. Batters have more control over their BABIP than pitchers do, and batter BABIP is often compared to their career BABIP, where pitchers are compared to league average to indicate luck.
O-Swing%: The percentage of pitches a batter swings at outside the strike zone.
Z-Swing%: The percentage of pitches a batter swings at inside the strike zone.
Swing%: The overall percentage of pitches a batter swings at.
O-Contact%: The percentage of pitches a batter makes contact with outside the strike zone when swinging the bat.
Z-Contact%: The percentage of pitches a batter makes contact with inside the strike zone when swinging the bat.
Contact%: The overall percentage of a batter makes contact with when swinging the bat.
Zone%: The overall percentage of pitches a batter sees inside the strike zone.
F-Strike% – The percentage of first pitch strikes.
SwStr%: The percentage of total pitches a batter swings and misses on.
There are two versions of plate discipline data. Raw PitchF/x data, and manually adjusted data. PitchF/x data is more consistent in values from year to year.
– (FanGraphs Wins Above Replacement). WAR is the complete measure of a players contributions to their team. Position players WAR
is calculated from batting, running, and fielding. It adds wRAA(adjusted for park), UZR, and BSR. It then adds a replacement value (see next point) and a positional adjustment (see below) for a total number of runs above replacement (RAR). Runs are then converted into wins. It is generally accepted that 10 runs = 1 win (it is usually a little less than 10). The WAR value means how many more wins that the player contributed for his team than a replacement player from AAA would produce. Pitchers WAR
is the same concept as hitters, except that it is only based on FIP and park factors. WAR on a team scale should correlate highly to actual wins.
– A concept that that is determined to be a player that is readily available in AAA. A team made up of replacement players should theoretically win 47.7 or 48 games in a season.
– It is well known by everyone in baseball that some positions are easier to play than others. 1B is much easier to play than SS, CF is harder than LF and RF, etc. Positional adjustment accounts for the difficulty of playing certain positions and this is used in WAR calculations.
– Not all baseball stadiums are created equally. They all have different dimensions and this affects results. A fly ball to left in Fenway usually turns into a double. The thin air in Colorado allows the ball to travel much farther. Differences in parks are accounted for and the factors can be found here
– Baseball-Reference’s version of WAR. Click the link for information on differences from fWAR.