How to Read a Player Comparison Page

Baseball Data Hub has more than 4,000 head-to-head pages, each putting two careers side by side. They are built to answer a narrow question quickly, such as whether Barry Bonds or Babe Ruth was the better hitter, while leaving the full record a click away. This guide walks through a page from top to bottom.

Hitters, pitchers and one of each

Each player is classed as a hitter or a pitcher from his career line: he counts as a pitcher if he threw at least 20 innings and had fewer at-bats than innings pitched. Babe Ruth, who began his career as a pitcher, compares as a hitter by that rule, because he batted far more often than he pitched.

Two hitters are compared on batting statistics and two pitchers on pitching statistics. When a hitter meets a pitcher, the page cannot score the two on the same categories, so it shows each player's career in his own role, in two separate tables, and compares them on PIV, the site's value measure, which is on the same scale for both.

The scoreline

The box at the top reads like a result: one player "leads 7 of 11 scored categories", or the pair is "even" across them. It counts the rows of the stat table in which each player is ahead. Rows where the two are exactly level count as ties and are included in the total. When both players lead the same number of rows, the scoreline says "even", and the written verdict further down uses PIV to decide between them.

Which rows are scored

Not every row counts. For most statistics more is better: hits, home runs, on-base percentage, strikeouts by a pitcher. For a few, less is better, and the page scores them that way: a lower ERA, a lower WHIP and fewer walks per nine innings win.

Some rows are not scored at all, because neither more nor fewer is an achievement. A hitter's strikeouts, and a pitcher's losses, walks, hits allowed and home runs allowed, mostly track how long a career lasted. A longer career piles up more losses as well as more wins, and it would make no sense to award the shorter career a category for having fewer. These rows are still shown so the table is complete, but they carry a "not scored" tag and never affect the scoreline.

The side-by-side table

The career table marks the leader of each scored row with an arrow. The totals are the same figures the players' own profile pages show: comparison pages and profiles are built from the same career tables in the same build, so the two cannot disagree. When a player is still active, the table says so and gives the date his totals run through.

Counting totals favor the longer career. When two careers differ a lot in length, the rate rows, such as batting average, on-base percentage, slugging and OPS for hitters and ERA, WHIP and strikeout rate for pitchers, usually say more about how good each player was while he played.

PIV and peak seasons

Below the table, the PIV section compares the two careers on the site's era-adjusted value measure. PIV is calculated from completed seasons, so the section states which season it runs through. For an active player it can be a season behind his counting totals.

The peak seasons section lists each player's three best years: by OPS for hitters, among seasons with at least 300 at-bats, and by ERA for pitchers, among seasons with at least 120 innings. A season still in progress is labelled as such. Peaks are a useful check on a lopsided career total, because a player with a shorter career can still have had the best individual seasons.

Comparing an active player

When one of the two players is still active, the page is a snapshot. His totals run through the date the page gives, his PIV through the last completed season, and his peak seasons can still change. A current player set against a retired star will usually trail in counting totals simply because his career is not over, so until it is, the rate rows and the peak seasons are the fairer test.

How matchups are chosen

The pairs are not random. The comparison hub groups them by the argument each one settles:

• Marquee Matchups: a short hand-picked list of the most-asked comparisons, such as Mays and Aaron.
• Hall of Famer vs Hall of Famer: pairs of Hall of Fame inductees.
• Same-Era Rivals: players whose careers overlapped for at least eight seasons.
• Longtime Teammates: players who shared a club for at least five seasons.
• Today vs the All-Time Greats: current players measured against retired stars.
• Baseball Families: fathers, sons and brothers.

A player needs a substantial career to be paired at all, such as 1,500 plate appearances for a hitter or 800 innings for a starting pitcher, with lower bars for active players, whose careers are still being built.

Other ways to compare

A comparison page measures two careers as they happened. The Era Translator answers a different question: what a player's season would look like in another era's run environment. And for any single category, the leaderboards rank every player at once. The qualification guide explains how those boards decide who is eligible.