The Arizona Fall League — which league features a non-negligible portion of baseball’s top prospects — began yesterday in the Greater Phoenix Area and continues until mid-November. As suggested by how Mike Trout was more or less the worst player in 2011’s edition of the AFL — less than a year, it should be noted, before recording the best WAR in all of major-league baseball — there are limits to what any one player’s numbers might reveal about his true talent. That said, the numbers do reveal how the player is performing in the AFL itself — and what follows is intended for that particular end, if probably none other.

Below is a collection of the top-10 game scores both for pitchers and hitters from opening day of this year’s AFL. The equations for the scores are based on alterations Tom Tango has made to Bill James’s classic model. As with Tango’s scores, those which follow are intended to mimic roughly win percentage — such that a game score of 50 is equivalent roughly to a .500 winning percentage; a score of 70, a .700 winning percentage; and a score of 35 or thereabouts, replacement level.

Here are the relevant equations:

Pitcher Scores: 0.2 * TBF + 3 * (K – BB) + 35
Batter Scores: 3 * PA + (13 * HR + 3 * BB – 2 * K) + 35

The pitcher scores are based on kwERA, an ERA estimator which utilizes only strikeouts and walks as its inputs and which serves a preferable alternative to FIP in small samples, as home-run rates require more than a 1,000 batters faced to become reliable. The batter scores are based on a sort of offensive version of FIP and (accordingly) exclude base hits of any sort, as those also require a much larger samples to become reliable.

Top Pitcher Game Scores
Here are the pitching game scores from opening day in the Arizona Fall League, calculated according to the methodology above.

Top Batter Game Scores
Here are the batting game scores from opening day of the Arizona Fall League, also calculated according to the (potentially flawed) methodology above.

Three Notes of Assorted Merit

• By the methodology used here, Seattle’s Taijuan Walker produced the most impressive opening day among all AFL pitchers — not surprising, perhaps, both because (a) he’s talented and also (b) he (along with Washington’s Felipe Rivero) were the only pitchers to record at least four innings.
• Arizona’s Peter O’Brien led all opening-day hitters by game score, recording both a home run and a walk (along with a strikeout) in four plate appearances. O’Brien received one of the top-10 WAR projections for 2015 among all rookie-eligible players.
• Kansas City right-hander Kyle Zimmer, also previously among those prospects with promising WAR projections, also started on Tuesday after making his 2014 debut only in mid-August following a lingering lat injury.