they used the wrong term in the subtitles: RBI is "runs batted in". the term they meant to use was Batting Average, which is calculated by Hits / At Bats. a good batting average is usually anything over .300. Haruichi has gotten a hit every single at bat he has had in a game so far, making his batting average 1.000 (and by extension his On Base Percentage is 1.000 as well). making him (statistically) the most consistent offensive performer on Seido