WAR (Wins Above Replacement) summarizes a player's total value in wins versus a replacement-level player called up from AAA. It bundles hitting, defense, baserunning, and pitching into one number.
FanGraphs publishes fWAR; Baseball-Reference publishes bWAR. They differ on defensive metric (UZR vs DRS) and pitching philosophy (FIP vs RA), but the rankings mostly agree.
Reference: 2 is solid regular, 4 is All-Star, 6+ is MVP, 10+ is historic. Pitchers max around 7–8 WAR — 6 is already Cy Young territory.
Shohei Ohtani's 2021 fWAR surpassed 9 (hitting + pitching combined) — a historic level. Yu Darvish and Hideki Matsui sit among the all-time leaders in career WAR for Japanese MLB players.
→ Related: wRC+ / FIP / OPS+ & ERA+