To figure out what this is all about—yes, this is the ever-so-exciting discussion about the player uniform rules—we turn to Official Baseball Rule 3.03 (OBR is used in the WBC) and find that only one provision of the rule concerns buttons: "(h) Glass buttons and polished metal shall not be used on a uniform." NCAA Rule 1-14-e is the only uniform rule in any code to specifically mention buttoning or zipping up a uniform top, but that only pertains to a pitcher wearing a jacket while being a baserunner.
Other than that scenario, it appears HP Umpire Hernandez may have practiced some preventative officiating—addressing a potential safety or rules issue to prevent oddities from occurring later on as a result of the unbuttoned shirt. OBR 5.06(c)(7), for instance, discusses lodged balls or balls that find their way into a player's uniform—if a ball were to go into Quijada's shirt, for instance, the resulting penalty would be a one base award for the batter and all baserunners (if deemed inadvertent). The MLB Umpire Manual further expands OBR 5.06(c)(7) to apply to batted and thrown, in addition to pitched, balls.
Video as follows:
Alternate Link: Angel Hernandez tells Venezuela pitcher to button up during WBC game (CCS)
