wOBA — Weighted On-Base Average
Not all ways of reaching base are equal: a home run is worth far more than a walk. wOBA assigns each outcome its real run value, derived from decades of play-by-play data, and rolls them into a single rate scaled to look like OBP. A .370 wOBA is excellent; .320 is average. It is the cleanest single measure of offensive value per plate appearance.
wRC+ — Park and League Adjusted
Weighted Runs Created Plus takes wOBA and adjusts it for the ballpark and the run environment of the era, then sets the league average to exactly 100. A 140 wRC+ means a hitter created 40 percent more runs than average; an 80 means 20 percent fewer. Because it is normalised, you can compare a hitter in pitcher-friendly Oakland directly with one in hitter-friendly Coors Field.
WAR — Wins Above Replacement
WAR bundles hitting, baserunning, fielding, and (for pitchers) run prevention into an estimate of how many wins a player adds compared with a freely available replacement-level substitute. A 2-WAR player is a solid regular; 5 is an All-Star; 8-plus is an MVP season. WAR is imperfect and version-dependent, but it is the closest thing to a single currency for player value.
Why the Model Cares
These park- and context-adjusted metrics let the Ra model compare lineups fairly across thirty very different stadiums — the foundation of an honest matchup projection.