Baseball terminology is confusing. Here are definitions and explanations of the statistics used in this project:

- Wins Above Replacement (WAR): Imagine if there could be one number to represent a player’s performance over time. This one number could encapsulate everything a player does. It could track hitting, pitching, baserunning, and fielding. WAR is that one number. The formula is very complicated, but WAR is the best way to sum up the performance of a player. It is measured in wins above a replacement-level player. A higher number is better. Phillies outfielder Bryce Harper accrued 5.9 WAR in 2021 according to Baseball Reference, meaning that if a replacement-level player was substituted for Harper for a whole season, the Phillies would have won about 5.9 fewer games. For more on WAR, see the Methodology tab in the About section.
- Batting Average: The number of hits a player records divided by the number of at-bats he has. A higher number is better.
- Earned Run Average (ERA): Take the number of earned runs charged to a pitcher and divide it by the number of innings pitched. That quantity multiplied by nine is a pitcher’s ERA. A lower number is better. An earned run is a run that scored without the help of an error or passed ball.
- Weighted On-Base Average (wOBA): From the MLB website: “wOBA is a version of on-base percentage that accounts for how a player reached base — instead of simply considering whether a player reached base. The value for each method of reaching base is determined by how much that event is worth in relation to projected runs scored (example: a double is worth more than a single). For instance: In 2014, a home run was worth 2.101 times on base, while a walk was worth 0.69 times on base. So a player who went 1-for-4 with a home run and a walk would have a wOBA of .558 — (2.101 + 0.69 / 5 PAs).” A higher number is better.
- Defensive Runs Saved (DRS): Again, from mlb.com: “DRS quantifies a player’s entire defensive performance by attempting to measure how many runs a defender saved. It takes into account errors, range, outfield arm and double-play ability. . . DRS uses Baseball Info Solutions data to chart where each ball is hit. Say, for instance, a center fielder sprints to make a nice catch on a fly ball. Then, say data from BIS tells us that similar fly balls get caught 60 percent of the time. That center fielder gains, essentially, 0.4 bonus points for difficulty. If he can’t make the play, he loses 0.6 points. At the end of the day, that player’s overall score gets adjusted to the league average — and then that score gets adjusted for how many runs the once-adjusted score is worth.” A higher number is better.
- Ultimate Zone Rating (UZR): This is essentially the same as DRS, but it uses a slightly different formula.
- Outs Above Average (OAA): A Statcast tool that measures the range of fielders to calculate how many outs a player has saved. It is calculated differently for infielders and outfielders. A higher number is better.
- On-Base Percentage (OBP): The number of hits, walks, and hit-by-pitches a player has divided by the number of plate appearances. A higher number is better. A higher number is better.
- Slugging Percentage (SLG): Like batting average, but each hit is weighted based on the number of bases the player advances. Formula: (Singles+ 2(Doubles)+ 3(Triples)+ 4(Home Runs)) / At-bats. A higher number is better.
- On-Base Plus Slugging Percentage (OPS): OBP + SLG.
- Fielding Independent Pitching (FIP): via mlb.com: “FIP is similar to ERA, but it focuses solely on the events a pitcher has the most control over — strikeouts, walks, hit-by-pitches and home runs. It entirely removes results on balls hit into the field of play. For example: If a pitcher has surrendered a high average on balls in play, his FIP will likely be lower than his ERA. Balls in play are not part of the FIP equation because a pitcher is believed to have limited control over their outcome.” A lower number is better.
- Runs Batted In (RBI): A batter is credited with an RBI when a run scores as a result of his plate appearance. This excludes cases where the runner hits into double plays or reaches on errors. Accumulating a greater number of RBIs is better.
- Win: When a team takes the lead and does not relinquish it, the pitcher who was on the mound at that time is credited with the win. Starting pitchers must complete five innings to earn a win. Accumulating a greater number of wins is better.
- WHIP: WHIP stands for “(walks plus hits) divided by innings pitched”, and that’s exactly the formula. A lower number is better.
- OPS+: From the MLB website: “OPS+ takes a player’s on-base plus slugging percentage and normalizes the number across the entire league. It accounts for external factors like ballparks. It then adjusts so a score of 100 is league average, and 150 is 50 percent better than the league average.”