Every abbreviation used on the site

Every stat column used across Inside the Pen, defined in plain language.

Pitcher Page: Cumulative Stats

The Cumulative Stats table at the top of each pitcher page shows season-level performance. If multiple seasons are available, both are displayed for comparison.

Column	Definition
Season	The year of the stats displayed. A "Spring" label indicates spring training data.
G	Games Pitched. Total number of games the pitcher appeared in.
ERA	Earned Run Average. The average number of earned runs a pitcher allows per 9 innings. Lower is better. Calculated as (Earned Runs / Innings Pitched) x 9.
IP	Innings Pitched. Total innings thrown, displayed to one decimal (e.g., 23.1 means 23 and one-third innings).
PA	Plate Appearances. Total number of batters the pitcher has faced.
P/pa	Pitches per Plate Appearance. Average number of pitches thrown to each batter. A lower number generally means the pitcher is more efficient.
SO/pa	Strikeouts per Plate Appearance. Shown as a percentage. Indicates how frequently the pitcher records a strikeout.
BB/pa	Walks per Plate Appearance. Shown as a percentage. Indicates how frequently the pitcher issues a walk. Lower is better.
HR/pa	Home Runs per Plate Appearance. Shown as a percentage. Measures how often the pitcher gives up home runs.
SB/pa	Stolen Bases per Plate Appearance. Shown as a percentage. Reflects the frequency of stolen bases allowed while this pitcher is on the mound.
G/AO	Ground Outs to Air Outs ratio. A value above 1.00 means the pitcher induces more ground balls than fly balls, which is generally desirable for relievers.
AVG	Batting Average Against. The batting average opposing hitters have recorded against this pitcher. Displayed to three decimal places.
OBP	On-Base Percentage Against. The rate at which opposing batters reach base (hits, walks, hit-by-pitch) against this pitcher.
xWOBA	Expected Weighted On-Base Average. A Statcast metric that estimates how well batters have hit the ball based on exit velocity and launch angle, removing the influence of defense and luck. Lower is better for pitchers.
OPS	On-Base Plus Slugging Against. OBP + Slugging Percentage allowed. A combined measure of how much offensive production the pitcher allows.

Premium members also see Home/Away and vs Left/vs Right splits below the main season row.

---

Pitcher Page: Advanced Stats (Premium)

The Advanced Stats table provides deeper analytics for each pitcher, with up to two seasons shown for trend comparison. This section is available to premium members.

Column	Definition
Season	Year of the stats, with the most recent season listed first.
G	Games Pitched.
IP	Innings Pitched.
ERA	Earned Run Average.
WHIP	Walks + Hits per Inning Pitched. Measures how many baserunners a pitcher allows per inning. A WHIP under 1.00 is elite; under 1.20 is very good. This is one of the most widely referenced relief pitcher stats.
FIP	Fielding Independent Pitching. Estimates a pitcher's ERA based only on events the pitcher controls: strikeouts, walks, hit-by-pitches, and home runs. Removes the influence of defense. Lower is better.
xFIP	Expected Fielding Independent Pitching. Same as FIP but normalizes home run rate to the league average, providing a better indicator of future performance. Lower is better.
K%	Strikeout Percentage. The percentage of plate appearances that end in a strikeout. Higher is better for pitchers.
BB%	Walk Percentage. The percentage of plate appearances that end in a walk. Lower is better.
SwStr%	Swinging Strike Percentage. The percentage of total pitches that result in a swinging strike. A key indicator of a pitcher's ability to miss bats. Above 12% is considered very good.
GB%	Ground Ball Percentage. The percentage of batted balls that are ground balls. Ground ball pitchers tend to allow fewer home runs and extra-base hits.
xWOBA	Expected Weighted On-Base Average. A quality-of-contact metric based on exit velocity and launch angle. Removes defense and luck. Lower is better for pitchers.
SV	Saves. A save is credited to a relief pitcher who finishes a game won by their team under specific conditions (typically entering with a lead of 3 runs or fewer).
SVO	Save Opportunities. The number of times a pitcher entered the game in a save situation, regardless of whether they converted. SV / SVO indicates save conversion rate.
HLD	Holds. A hold is credited to a relief pitcher who enters in a save situation, records at least one out, and leaves without relinquishing the lead. An important stat for setup men and middle relievers.

---

Pitcher Page: Tendency Classifications (Premium)

The Pitcher Tendency panel below the Advanced Stats table classifies each pitcher across six dimensions. When both current and prior season data exist, a tabbed view lets you switch between current-year analysis and a blended two-year view. The blended view weights each season by total batters faced, giving more influence to the larger sample.

Classification	How It Works	Tiers
Batted Ball	Based on Ground Ball Percentage (GB%). Indicates whether the pitcher primarily induces ground balls, fly balls, or a mix. Ground ball pitchers tend to allow fewer home runs.	Ground Ball (GB% > 50%) / Neutral (35 to 50%) / Fly Ball (< 35%)
Strikeout	Based on Strikeout Percentage (K%). Measures how frequently the pitcher records strikeouts relative to plate appearances.	Elite (> 30%) / Above Avg (25 to 30%) / Average (20 to 25%) / Below Avg (< 20%)
Command	Based on the K/BB ratio (strikeout rate divided by walk rate). Measures a pitcher's ability to miss bats while limiting free passes. A high K/BB ratio is one of the strongest indicators of pitching quality.	Elite (> 4.0) / Strong (3.0 to 4.0) / Average (2.0 to 3.0) / Poor (< 2.0)
Platoon	Compares the pitcher's OPS allowed against left-handed batters vs. right-handed batters. A meaningful gap indicates the pitcher is significantly more effective against one side. Uses a .040 OPS differential threshold.	Stronger vs LHB / No Platoon Split / Stronger vs RHB
Avg Fastball	Classifies the pitcher's average fastball velocity for the current season (using the faster of their four-seam or sinker). Velocity is shown in parentheses.	Elite Velo (> 97 mph) / Above Avg (94 to 97) / Average (91 to 94) / Below Avg (< 91)
Top Fastball	Classifies the pitcher's peak fastball velocity. This reflects the pitcher's top-end arm speed and ability to reach back for extra when needed. Velocity is shown in parentheses.	Elite Top-End (> 100 mph) / Above Avg (97 to 100) / Average (94 to 97) / Below Avg (< 94)

---

Pitcher Page: Advanced Pitcher Traits

The sidebar on each relief pitcher page lists behavioral traits derived from historical usage. These are shown for relievers only, not starters.

Trait	Definition
Opens Games	How often the pitcher enters in the 1st inning.
Avg Inning When Called	The typical inning the pitcher enters the game.
Pitches vs Lefties / Righties	Frequency of usage against each side of the plate (Yes / Rarely / Almost Never).
30+ Pitch Outings	Whether the pitcher regularly throws extended outings.
Before 8th Inning	Whether the pitcher is used in early or middle innings.
Back-to-Back Games	How often the pitcher appears in consecutive games.

---

Pitcher Page: Game Log Columns

The Game Logs table shows a pitcher's individual outings, sorted most recent first. The first 8 games display by default; click "Show all games" to expand.

Column	Definition
Game Date	The date of the game, followed by the pitcher's team abbreviation in parentheses.
Opponent	The opposing team, prefixed by "vs" (home) or "@" (away).
IP	Innings Pitched in that game. The superscript number (if present) indicates the inning in which the pitcher entered.
PA	Plate Appearances (batters faced) in that outing.
R	Runs allowed (earned and unearned).
H	Hits allowed.
2B	Doubles allowed.
3B	Triples allowed.
HR	Home Runs allowed.
BB	Walks (bases on balls) issued.
SO	Strikeouts recorded.
SB	Stolen Bases allowed while this pitcher was on the mound.
CS	Caught Stealing. Baserunners thrown out attempting to steal while this pitcher was on the mound.
NP-S	Number of Pitches and Strikes. Displayed as "Pitches-Strikes" (e.g., "24-17" means 24 pitches, 17 of which were strikes).
AVG	Batting Average Against for that specific outing.

---

Bullpen Usage Table Columns

The Bullpen Usage table appears on team pages and individual pitcher pages. It shows the last 7 days of bullpen activity at a glance and is fully sortable by column header.

Column	Definition
Player	The pitcher's name, linked to their individual pitcher page. A Swing tag indicates a flexible role pitcher.
IP	Total Innings Pitched over the last 7 days.
G	Games over the last 7 days.
ERA	ERA calculated from the last 7 days of outings only. Rolling short-term ERA, not the full season number.
FIP	Fielding Independent Pitching over the last 7 days.
EFF	Effectiveness Rating (0 to 100). Color-coded so green means strong and red means weak.
FTG	Fatigue Factor. Higher value means more recent workload.
Arsenal	Color-coded pitch-type badges. Opacity reflects usage rate.
Day Columns (dates)	Each day column shows two values stacked: IPIn (innings pitched with the inning entered as a superscript) and NP-S (pitches-strikes). An empty cell means no appearance that day. A green tint marks spring training games.

---

Pitch Arsenal Columns

The Pitch Arsenal section on each pitcher page includes a doughnut chart of pitch mix plus a detailed velocity and spin table.

Column	Definition
Pitch	The pitch type, shown as a full name with the abbreviation in parentheses. Common types: FF (Four-Seam Fastball), SI (Sinker), FC (Cutter), SL (Slider), CH (Changeup), CU (Curveball), SV (Sweeper), ST (Sweeping Curve), FS (Splitter), KC (Knuckle Curve).
Velo	Average Velocity in miles per hour for that pitch type during the current season.
Spin	Average Spin Rate in revolutions per minute (RPM). Higher spin on fastballs generally means more "rise" and missed bats. Spin effects vary by pitch type.
Usage	The percentage of total pitches that are this pitch type during the current season.

The Avg Fastball callout in the bottom-right of the arsenal section shows the pitcher's average fastball velocity, using the faster of their four-seam (FF) or sinker (SI).

---

Team Page Metrics

Effectiveness Rating. A proprietary 0 to 100 scale measuring overall pitcher effectiveness based on multiple performance indicators. Displayed on pitcher cards and the team summary. Higher is better.

Fatigue Factor. A measure of cumulative workload that accounts for recent innings pitched, pitch count, days of rest, and back-to-back appearances. Higher fatigue means the pitcher has been used more heavily and may be less available. Displayed as an inverted value on team pages (lower bar = more fatigued).

Overall Rating. A combined metric that blends effectiveness and fatigue into a single number. The primary "at a glance" indicator of a pitcher's current value to the bullpen.

Snapshot Power Rank. A ranking of every team's bullpen based on the most recent 7 to 10 days of work.

Season Long Power Rank. A ranking of every team's bullpen based on the full season body of work. Shorter streaks have minimal impact.

---