Expected runs (xR)

Three singles in one inning score a run. Three singles spread over three innings usually don't. Expected runs (xR) asks how many runs a team's plate appearances in a game would score on average, whatever order they came in.

Each game's plate appearances are replayed many times in random order, and the runs scored are averaged. From the same replays comes a postgame win expectancy: the share of replays in which the team outscored its opponent.

• xR well below the runs a team scored means its hits came at the right moments. Well above means it left runs on base.
• win_exp runs from 0 to 1. A team that won with a win_exp of 0.20 was outplayed and won anyway.
• Over a season, xR is a steadier read of an offense or a pitching staff than runs. It is what feeds AdjO and AdjD.

• team/{team_name}/game-log: xR, opp_xR and win_exp for each game of a season.
• box-score/{game_id}: expected, with xR by inning for both teams.

• It needs play-by-play, so a game without it has no xR.
• It treats the order of plate appearances as luck. Over one game, that removes real things too, like a pitcher tiring.