The left-on-left specialist — a left-handed reliever who sometimes faces only one left-handed hitter — soon might be an endangered species in Major League Baseball.



As part of a Jan. 14 proposal to the players’ union on pace of play, baseball suggested a rule requiring pitchers to face a minimum of three batters, sources told The Athletic.



The Major League Baseball Players Association responded last Friday with its own comprehensive proposal that addressed the players’ concerns on competitive integrity and service-time manipulation in multifaceted fashion, sources said. A lowering of a team’s draft position for failing to reach a specified win total in a certain number of seasons is believed to be part of the union’s plan.



A universal designated hitter — something the players have sought for more than three decades, according to commissioner Rob Manfred — also was part of the union’s proposal. Under the...