Metrics

Reference for every stat the app can plot, plus the Min PA / IP knob that filters per-season data before the curve is fit. All formulas use the abbreviations as they appear in the underlying MLB Stats API.

Batting metrics

For batters, the weight column in the weighted least-squares fit is PA (plate appearances). Anchor points below are full-season values for full-time players.

AVG — Batting average

Hits per at-bat:

AVG = H / AB

A decimal between 0 and 1.

Range Read
.300+ Excellent
.275 Solid regular
.250 Average MLB hitter
.220 Below average

OBP — On-base percentage

Fraction of plate appearances where the batter reached base by hit, walk, or hit-by-pitch:

OBP = (H + BB + HBP) / (AB + BB + HBP + SF)

Where SF = sacrifice flies. OBP excludes errors and fielder’s choices.

Range Read
.400+ Elite
.360 All-Star
.330 Solid regular
.300 Below average

SLG — Slugging percentage

Total bases gained per at-bat. A double counts as 2, a triple as 3, a home run as 4:

SLG = (1B + 2·2B + 3·3B + 4·HR) / AB
Range Read
.500+ Power hitter
.450 Strong power
.400 Average
.350 Limited power

OPS — On-base + Slugging

The sum of OBP and SLG. The single most-used summary of offensive value:

OPS = OBP + SLG
Range Read
.900+ All-Star tier
.800 Above average
.700 Average
.600 Below average

HR — Home runs

The count of home runs in a season — a raw total, not a rate stat. The curve fits this against age directly.

Range Read (full season)
40+ Elite power
30 Power hitter
20 Full-time regular
10 Part-time / contact

ISO — Isolated power

Pure extra-base power, with singles’ contribution removed:

ISO = SLG − AVG

A batter who hits only singles has SLG = AVG and therefore ISO = 0.

Range Read
.250+ Elite power
.200 Power threat
.150 Average
.100 Light power

Pitching metrics

For pitchers, the weight column is IP (innings pitched). All per-9 rates multiply by 9 to extrapolate to a full game’s worth of innings.

ERA — Earned run average

Earned runs allowed per 9 innings:

ERA = 9 × ER / IP

Where ER excludes runs that scored after a fielding error. Lower is better.

Range Read
<2.00 Cy Young tier
3.00 All-Star
4.00 Solid regular
5.00+ Below average

WHIP — Walks + Hits per Inning Pitched

Baserunners allowed per inning:

WHIP = (BB + H) / IP

Lower is better.

Range Read
<1.00 Elite
1.20 All-Star
1.30 Solid regular
1.40+ Below average

K/9 — Strikeouts per 9 innings

K/9 = 9 × K / IP

Higher is better.

Range Read
11+ Power pitcher
9.0 Strong
7.0 Average
5.0 Contact pitcher

BB/9 — Walks per 9 innings

BB/9 = 9 × BB / IP

Lower is better (better control).

Range Read
<2.0 Elite control
2.5 Strong
3.5 Average
5.0+ Wild

HR/9 — Home runs per 9 innings

HR/9 = 9 × HR / IP

Lower is better.

Range Read
<0.8 Elite
1.0 Strong
1.2 Average
1.5+ Homer-prone

Min PA / IP per season

The Min PA / IP per season knob in the sidebar drops per-season rows from the curve fit when they fall below a minimum playing-time threshold. The unit follows the Position toggle:

  • PA (plate appearances) when Position is Batter.
  • IP (innings pitched) when Position is Pitcher.

It exists because a 50-PA September call-up or a 20-IP injury year carries almost no signal about a player’s true ability. A weighted quadratic fit will still treat such a row as a data point (lightly weighted, but present), and very-low-weight seasons can drag the fit when they’re outliers. Setting a minimum drops those rows entirely.

Common thresholds

Value What it represents
502 PA The official batting-title qualification (3.1 PA × games scheduled).
162 IP The official ERA-title qualification (1 IP × games scheduled).
300 PA / 100 IP Typical “full-time regular” lower bound.
100 The default; keeps most non-trivial seasons.
0 Disables the filter — every season counts toward the fit.

For a player whose role changed substantially over time (starter-turned-reliever, regular-turned-bench), tuning this knob up to focus on their prime role often gives a cleaner curve. For a young player with only a few full seasons, tune it down to include near-rookie years.

See also

  • Modeling approach — how the quadratic fit uses these metrics as the response variable, and how weights are applied.
  • Methods — worked example using OPS for Mickey Mantle, with the centered-form interpretation.