Alex Bregman probably thought he was speaking for all of his fellow baseball players when, in a session with reporters at the All-Star Game in Cleveland this month, he made an emphatic proclamation.

“All the hitters care about now is OPS,” said Bregman, the Houston Astros third baseman. “We don’t care about batting average.” He was referring to on-base plus slugging, the modern metric that, unlike batting average, takes walks into account and values extra-base hits more than singles. Bregman went on to describe batting average,...