All content on this site (including text, graphs, and any other original works), unless otherwise noted, is licensed under a
Creative Commons
License.
Because we like baseball, we like statistics. Baseball statistics, that is. You can thoroughly enjoy baseball without paying any attention to its statistics, of course. But to really understand the game deeply, you’ve got to dive in. That’s why the Hardball Times site tracks a wealth of baseball stats throughout the year, thanks to our business partners, Baseball Info Solutions.
Following is a definition of most of the stats we use. All of the source statistics listed here are reported by Baseball Info Solutions, though we perform most of the calculations ourselves. By the way, when you see a writer refer to a batter’s performance in this way -- .275/.338/.425 (insert your own numbers) – he’s referring to the batter’s BA/OBP/SLG. If you’re not sure what those are, read on.
Batting Average on Balls in Play. This is a measure of the number of batted balls that safely fall in for a hit (not including home runs). The exact formula we use is (H-HR)/(AB-K-HR+SF) This is similar to DER, but from the batter's perspective.
Walks Allowed per games pitched. This stat is based on the number of walks allowed divided by total number of batters faced, times the average number of batters per game in that specific league (generally around 38 batters a game).
A run contribution formula created by David Smyth, which quantifies the number of runs contributed by a batter. The fundamental formula for Base Runs is (baserunners times scoring rate) plus home runs. This article, among others, has found that Base Runs is the best run contribution formula. You can read more about it in this Wiki entry.
"Clutch" is the name we've given to the portion of Bill James's Runs Created formula that includes the impact of a batter's batting average with runners in scoring position and the number of home runs with runners on. The specific formula is Hits with RISP minus overall BA times at bats with RISP, plus HR with runners on minus (all HR/AB) times at bats with runners on. This stat is not a definitive description of "clutch hitting," just one way of looking at it.
Often stands for College World Series, but it's Career Win Shares in our stats. Our methodology for calculating Win Shares after 2003 differs somewhat from Bill James's original formula.
Defense Efficiency Ratio. The percent of times a batted ball is turned into an out by the teams’ fielders, not including home runs. The exact formula we use is (BFP-H-K-BB-HBP-Errors)/(BFP-HR-K-BB-HBP). This is similar to BABIP, but from the defensive team's perspective. Please note that errors include only errors on batted balls.
Expected Win Shares are a playing time metric. They are the number of Win Shares a player would be expected to accumulate, given his playing time (including plate appearances, innining in the field, and innings pitched), if he were an average player. Expected Win Shares is a baseline for evaluating Win Shares totals, as in Win Shares Above Bench.
Fielding Independent Pitching, a measure of all those things for which a pitcher is specifically responsible. The formula is (HR*13+(BB+HBP-IBB)*3-K*2)/IP, plus a league-specific factor (usually around 3.2) to round out the number to an equivalent ERA number. FIP helps you understand how well a pitcher pitched, regardless of how well his fielders fielded. FIP was invented by Tangotiger.
G/F stands for Groundball to Flyball Ratio. It is the number of groundballs divided by the number of flyballs (but not line drives) hit by the batter or allowed by the pitcher. It includes all batted balls, not just outs.
Gross Production Average, a variation of OPS, but more accurate and easier to interpret. The exact formula is (OBP*1.8+SLG)/4, adjusted for ballpark factor. The scale of GPA is similar to BA: .200 is lousy, .265 is around average and .300 is a star. A simple formula for converting GPA to runs is PA*1.356*(GPA^1.77).
Home Runs as a percent of outfield flyballs. The home run totals are adjusted by the home ballpark's historic home run rates. Research has shown that about 11% to 12% of outfield flies are hit for home runs. For pitchers, significant variations from 11% are probably the result of "luck," but for hitters this stat is more indicative of a true skill (hitting the ball hard!).
Home Runs Allowed per games pitched. This stat is based on the number of home runs allowed divided by total number of batters faced, times the average number of batters per game in that specific league (generally around 38 batters a game).
Strikeouts per games pitched. This stat is based on the number of strikeouts divided by total number of batters faced, times the average number of batters per game in that specific league (generally around 38 batters a game).
Line Drive Percentage. Baseball Info Solutions tracks the trajectory of each batted ball and categorizes it as a groundball, fly ball or line drive. LD% is the percent of batted balls that are line drives. Line drives are not necessarily the hardest hit balls, but they do fall for a hit around 75% of the time.
Leverage Index, invented by Tangotiger, is a measure of how critical a specific batting situation is. One (1) is average, anything above one is more critical and anything less than 1 is less critical. You can read more about Leverage Index in Tango's three-part series on THT: (Part One, Part Two, and Part Three). Baseball Prospectus has its own definition of Leverage Index, but Tangotiger's (who originated the term) definition is better and more accurate.
LOB stands for Left On Base. It is the number of runners that are left on base at the end of an inning. LOB% is slightly different; it is the percentage of baserunners allowed that didn't score a run. LOB% is used to track pitcher's luck or effectiveness (depending on your point of view). The exact formula is (H+BB+HBP-R)/(H+BB+HBP-(1.4*HR)). You can read more about LOB% in this article.
The Marcels are a simple way of calculating a player forecast. Named after the monkey from Friends (so simple a monkey could do them), they simply consist of averaging a player's previous experience (with greatest weight on the most recent years) and regressing to the major league average depending on the number of years the player has been in the majors. This is done for each component (home runs, doubles, walks, etc.) A simple aging factor is applied, but no park factor.
On Base Percentage, the proportion of plate appearances in which a batter reached base successfully, including hits, walks and hit by pitches. OBP is also a powerful performance metric when interpreted as the percentage of times the batter didn't make an out.
Invented by Doug Drinen in the late 1990's, P measures the criticality of a reliever's appearance. It is computed by estimating the impact a successful relief appearance would have on a team's WPA. You can read more about P in The One About Win Probability and Closer.
Putouts, the number of times a fielder recorded an out in the field. First basemen and outfielders get lots of these. From a pitching perspective, PO stands for pick offs -- the number of times a pitcher picks a baserunner off a base.
Invented by John Thorn and Pete Palmer, this is a measure of the number of runs a pitcher saved compared to average. The formula is league-average RA/IP minus park-adjusted RA/IP, times total innings pitched. This is the same formula as Lee Sinins' RSAA (see below).
A new stat, created by our own David Gassko. The notion behind Pitching Runs Created is that a run saved is worth more than a run scored, and PRC puts runs saved on the same scale as runs scored. You can directly compare PRC to a batter's Runs Created to gauge each player's relative value to his team. You can read more about Pitching Runs Created in the introductory article and the follow-up article.
PrOPS stands for "Predicted OPS." It was developed by J.C. Bradbury amd introduced in this article. PrOPS isn't really a new stat; it's a formula for predicting what a player's OPS is likely to be in the future based on his batted balls, strikeouts, home runs and walks.
A formula for converting a team’s Run Differential into a projected Won/Loss record. The formula is RS^2/(RS^2+RA^2). Teams’ actual won/loss records tend to mirror their Pythagorean records, and variances can usually be attributed to luck.
You can improve the accuracy of the Pythagorean formula by using a different exponent (the 2 in the formula). In particular, a sabermetrician named US Patriot discovered that the best exponent can be calculated this way: (RS/G+RA/G)^.287, where RS/G is Runs Scored per game and RA/G is Runs Allowed per game. This is called the PythagoPat formula.
Runs Created. Invented by Bill James, RC is a very good measure of the number of runs a batter truly contributed to his team’s offense. The basic formula for RC is OBP*TB, but it has evolved into over fourteen different versions. We use the most complicated version, which includes the impact of hitting well with runners in scoring position, and is adjusted for ballpark impact. RC/G refers to Runs Created Per Game, which Runs Created divided by the number of outs made by the batter, times 27.
Runs Created Above Average. A stat invented and tracked by Lee Sinins, the author of the Sabermetric Baseball Encyclopedia. Lee calculates each player’s Runs Created, and then compares it to the league average, given that player’s number of plate appearances. Lee uses a different version of RC than we do, though the two are very similar.
Runs Saved Above Average. This stat, which is also tracked and reported by Lee Sinins, is a measure of a pitcher’s effectiveness and contribution. The formula is RA/IP minus league-average RA/IP, times total innings pitched.
Revised Zone Rating is the proportion of balls hit into a fielder's zone that he successfully converted into an out. Zone Rating was invented by John Dewan when he was CEO of Stats Inc. John is now the owner of Baseball Info Solutions, where he has revised the original Zone Rating calculation so that it now lists balls handled out of the zone (OOZ) separately (and doesn't include them in the ZR calculation) and doesn't give players extra credit for double plays (Stats had already made that change). We believe both changes improve Zone Ratings substantially. To get a full picture of a player's range, you should evaluate both his Revised Zone Rating and his plays made out of zone (OOZ). You can read more about the Revised Zone Ratings in this article.
Win Probability Added. A system in which each player is given credit toward helping his team win, based on play-by-play data and the impact each specific play has on the team's probability of winning. You can read more about WPA in The One About Win Probability.
Win Shares. Invented by Bill James. Win Shares is a very complicated statistic that takes all the contributions a player makes toward his team’s wins and distills them into a single number that represents the number of wins contributed to the team, times three. We have tweaked James’ original formula somewhat.
Win Shares Above Bench, or Baseline. WSAB is a refined approach to Win Shares, in which each player's total Win Shares are compared to the Win Shares an average bench player would have received, given that player's time at bat, on the mound or in the field.
This is an important adjustment to Win Shares, as we discovered during the 2003-2004 offseason. The bench player approach is explained in this article. It is essentially 75% of Expected Win Shares for all players except Starting Pitchers, for whom it is 60% of Expected Win Shares.
Win Shares Percent, a Win Shares "rate stat" -- a measure of the player's contribution, given his playing time. The math is WS/(2*ExpWS). Expected Win Shares are the number of Win Shares an average player contributed, given that particular player's time at bat, on the mound or in the field.
Expected Fielding Independent Pitching. This is an experimental stat that adjusts FIP and "normalizes" the home run component. Research has shown that home runs allowed are pretty much a function of flyballs allowed and home park, so xFIP is based on the average number of home runs allowed per outfield fly. Theoretically, this should be a better predicter of a pitcher's future ERA.
