Acronym Glossary

acronyms glossaryAs advanced stats continue to develop, fantasy baseball has become increasingly reliant on them. Sure, we still use the traditional 5×5 scoring in most leagues, but advanced stats allow us to look under the hood and determine whether or not a player’s stat line is supported by his skill set. Good fortune with batted balls falling for hits or a couple of HRs just barely clearing the fence can dramatically impact a player’s roto stat line.

Advanced stats are crucial for player analysis, but for a casual fantasy owner, articles that spew an endless stream of foreign acronyms can be a lot to take in. This glossary aims to serve as a guide for any and all acronyms and abbreviations commonly used at Fantasy Assembly.

Position Abbreviations
We all know the basic positions (I hope) but there are a lot of different roster settings out there, so some may not be familiar with certain position abbreviations that we fantasy writers tend to toss around.

CI – Corner Infielder – Any player eligible at either 1B or 3B.
MI – Middle Infielder – Any player eligible at either 2B or SS.
UTIL – Utility – Any hitter can be used here.

These abbreviations don’t really fit into another category, but are still important to know.

ROS – Rest of Season – This is just what it sounds like. You will often see this abbreviation during the season when the author is attempting to project results moving forward.

Simple Batting Stats

AB – At Bat – Plate appearance that does not end in a walk, a hit by pitch, a sacrifice, obstruction or interference.

BA – Batting Average – # of Hits divided by total ABs.

CS – Caught Stealing

GDP – grounded into double play

HBP – Hit by Pitch – Batter is awarded first base after being hit by a pitched ball.

OBP – On Base Percentage – OBP is the total number of (hits + walks + HBP) / (ABs + walks + HBP + sacrifice flies). It is important to note two distinctions from batting average. First, walks and HBP will help OBP, but not BA. Secondly, sacrifice flies will not count against BA, but it does count against OBP.

OPS – On Base + Slugging Percentage – OBP + SLG

PA – Plate Appearances – Total number of times a batter completes a turn at the plate.

SLG – Slugging Percentage – Total Bases / ABs

Advanced Batting Stats courtesy of

ISO – Isolated Power – ISO is a measure of a hitter’s power. It is calculated by slugging percentage – BA.

League average for ISO is about .140. A good power hitter will have an ISO above .200 and a player with an ISO below .100 might be accused of having little to no power.

BABIP – Batting Average on Balls in Play – Percentage for a “ball in play” falling safely for a hit. A “ball in play” is any plate appearance that does not end in a walk, HBP, strikeout, sacrifice bunt, interference, or a homerun.

League average for BABIP is approximately .300. Some articles may infer that hitters with a BABIP above .300 are “lucky”, but that is not necessarily true. Hitter skill can have a large impact on BABIP. Batters who hit a lot of line drives and fast runners who hit a lot of ground balls will generally have above average BABIPs. Conversely, fly ball hitters and slow-footed batters with high ground ball rates will likely post a below average BABIP.

wOBA – Weighted on Base Average – A comprehensive measure of a hitter’s value with the bat. I am not going to get into the calculations because they are very complex, but every possible outcome for a hitter is assigned a multiplier that relates to the probability that event leads to run production.

League average wOBA is around .320. Anything above .340 is considered to be very good and a wOBA below .300 is not so good. Some hitters with wOBA below .300 can still be fantasy relevant if they make a profound impact in HRs + SBs.

wRC+ – Weighted Runs Created – Another measure of a hitter’s value with the bat. This particular stat attempts to measure how many runs a player creates over the course of a season

wRC+ is scaled to 100. By definition, 100 is the league average. Each number above or below 100 indicates the percentage above or below league average. For example, a player with a wRC+ of 110 produced 10% more runs than an average player. A wRC+ of 80 would indicate they produced 20 percent less than the league average.

BB% – Walk Percentage – Walks / PA – Today, the league average walk rate is about 8%. Anything above 10% is considered very good and anything below 5.5% is considered poor. Walk percentage is a good indicator of a hitter’s plate discipline. Players with high walk rates are generally more likely to hit for a good batting average.

K% – Strikeout Percentage – Ks (strikeouts) / PA – Today, the league average strikeout rate is about 20%. Anything under 14% is considered very good and anything above 25% is considered poor. Players with high K rates are less likely to hit for a good batting average.

BB/K – Walk to Strikeout Ratio – BBs / Ks – League average BB/K ratio is approximately .40. Anything above .65 is considered very good, and anything below .30 is considered bad.

GB% – Ground Ball Percentage – Percentage of batted balls in play that end up as ground balls. GB / (Balls in play + Homeruns). League average GB% is 44%.

LD% – Line Drive Percentage – Percentage of batted balls in play that end up as line drives. LD / (Balls in play + Homeruns). League average LD% is 21%.

FB% – Fly Ball Percentage – Percentage of batted balls in play that end up as fly balls. FB / (Balls in play + Home runs). League average FB% is 35%.

HR/FB% – Home run per fly ball ratio – HR / FB – Ratio of home runs to fly balls.

The league average HR/FB% is about 9.5%, but it is important to weigh a hitter’s HR/FB% against their average fly ball distance to know whether or not a hitter has a flukey HR rate. Elite power hitters often have HR/FB rates above 20% and hitters with little power may have HR/FB rates under 5%.

IFH% – Infield Hit percentage – Infield hits / ground balls

BUH% – Bunt Hit percentage – Bunt hits / bunt attempts

Average Fly Ball Distance – A hitter’s average distance traveled for all batted balls classified as a fly ball. Top power hitters have average fly ball distances over 290 feet. The league average is about 278 feet. Anything under 270 feet is indicative of limited power.

Swing % – Percentage of pitches that a batter swings at. League average is about 46%

O-Swing % – Percentage of pitches outside the strike zone that a batter swings at. O-Swing is an important indicator of plate discipline. League average O-Swing is approximately 30%. Hitters with an O-Swing % greater than 35% might be classified as free swingers. An O-Swing % under 25% would be indicative of a patient approach.

Z-Swing % – Percentage of pitches inside the strike zone that a batter swings at. A high Z-Swing score would indicate that the hitter has an aggressive approach. A low score would signal patience. The league average Z-Swing is approximately 65%.

Contact % – Percentage of swings on which contact was made, including foul balls. League average contact % is about 80%. Anything below 76% is considered low, and anything above 84% is considered to be very good.

O-Contact % – Percentage of swings on pitches outside the zone on which contact was made. League average is about 66%. How much a hitter’s O-Contact score affects their overall contact rate will depend on how many pitches they chase. Also, a high O-contact % is not necessarily good. Contact made on pitches outside the zone can often be weak contact that leads to outs.

Z-Contact % – Percentage of swings on pitches inside the zone on which contact was made. League average is about 87%.

SwStr % – Swings and misses / total pitches- Percentage of total pitches that a batter swings and misses on. League average is about 9.5%.

Whiff Rate – Swings and misses / total swings- Whiff rate is the percentage of total swings that a batter swings and misses on. League average is about 20%.

Pitching Stats
Many of our hitter stats defined above can also be used for pitchers.
The context may be a little different, but the statistic is still the same.

Simple Pitching Stats

W – Win – In order to receive credit for the win, the pitcher’s team must take the lead and never relinquish it. The last pitcher to record an out for the winning team before the final lead change is credited with the win, unless the final lead change occurs before the end of the 5th inning and the pitcher is lifted before completing the 5th. In that case, the pitcher who recorded the final out of the 5th inning would be credited with the win.

L – Loss – The losing pitcher is responsible for the go ahead runner reaching base, even if by error. If the opposing team never relinquishes the lead, the pitcher is charged with a loss.

S – Save – In order for a pitcher to earn a save, they must log the final out for the winning team and they cannot be the pitcher of record. If both these things are true, then they need to meet one of the following criteria to get the save:

  • Enters game with a lead of 3 runs or less and works at least 1 full inning.
  • Enters game with the potential tying run on base, at bat or on deck.
  • Pitches 3 innings or more

BS – Blown Save – A relief pitcher enters the game in a save situation, and the opposing team either ties the game or takes the lead while he is on the mound. Blown saves can take place in any inning.

H or HLD – Hold – In order for a pitcher to earn a hold, he must appear in relief, must not be the pitcher of record, must record at least one out, and must be relieved by another pitcher without yielding the lead. In addition to all of that, one of the following criteria must be met:

  • Enters game with a lead of 3 runs or less and works at least 1 full inning.
  • Enters game with the potential tying run on base, at bat or on deck.
  • Pitches 3 innings or more

CG – Complete Games – When a starting pitcher goes the entire distance

ER – Earned runs allowed – Any run that was not enabled by a fielding error or a passed ball.

ERA – Earned Run Average – Earned runs * 9 / Innings Pitched – ERA is simply the number of earned runs a pitcher allows for every 9 innings pitched.

G – Games appeared in

GS – Games Started

IP – Innings Pitched

K – Strikeout

R – Runs allowed

ShO – Shutouts – Pitcher throws a CG, and the opposing team does not score.

TBF – Total Batters Faced

WHIP – Walks and hits per Inning Pitched – Walks + Hits / IP – This stat is a measure of pitcher efficiency commonly used in rotisserie leagues.

Advanced Pitching Stats – courtesy of

K/9 – Strikeouts per 9 innings – (K * 9) / IP – K/9 is sometimes used a roto category instead of Ks. This stat is a great way to see how efficiently a pitcher can pile up Ks. League average is about 7.1 K/9. A K/9 above 8.5 is very good and above 9.5 is dominant. Pitchers with K/9 rates below league average can be difficult to use in some formats.

BB/9 – Walks per 9 innings – (BB * 9) / IP – Walk rates are very important for pitchers. A high walk rate will negatively impact WHIP and eventually ERA also. 3.3 BB/9 is about average. Pitchers with a BB/9 under 2.3 are doing a great job limiting walks and pitchers with a BB/9 above league average can be risky assets.

K/BB – Strikeout per Walk Ratio – Ks / BBs – K/BB is another measure of pitcher efficiency. League average is about 2.15. Any K/BB rate above 3.00 is very good and a K/BB under 2.10 is not good.

K-BB% – Strikeouts minus walk percentage – (K% – BB%) – This stat is quickly gaining popularity and can be used instead of K/BB ratio. The idea is that some pitchers with extremely low walk rates tend to be somewhat overvalued using K/BB. League average K-BB% is about 10%. Anything above 15% is great, and anything below 8% is not so good.

LOB% – Left on Base Percentage, or Strand Rate – Percentage of base runners who have not been put out, yet still failed to score before the third out of the inning is recorded.

League average LOB% is about 72%. Anything above 78% is considered great, while anything below 65% is bad. When analyzing this stat, it is important to understand that some pitchers (especially ones with high K rates) will often post higher than average LOB% rates. In general, however, most pitchers will see their strand rate regress close to league average. A high strand rate could indicate that the pitcher has been lucky, while a low strand rate could indicate the opposite. Be careful though, because bad pitchers also tend to have a low LOB%.

FIP – Fielding Independent Pitching- Measures what a pitcher’s ERA would be with league average results on balls in play and average timing. In other words, FIP attempts to isolate the pitcher’s true talent. If a pitcher’s FIP is substantially higher than his ERA, this might indicate he may have had good luck. If FIP is substantially lower, it might signal bad luck. Keep in mind though, a pitcher with a great team defense behind him should be expected to consistently beat their FIP. Vice versa for a pitcher with a bad defense behind him.

xFIP – Expected Fielding Independent Pitching- This is an extension of FIP that also assumes a league average HR/FB rate. xFIP is a favorite ERA indicator of many fantasy analysts.

SIERA – Skill Interactive ERA- Yet another ERA indicator, this one is perhaps more accurate than xFIP because it factors in batted ball results. Using xFIP and SIERA together can help paint a pretty accurate picture of the pitcher’s true talent level.