Matthew Derrick Williams, nicknamed "Matt the Bat" and "the Big Marine", is an American professional baseball manager and former third baseman who is the third base coach for the San Francisco Giants of Major League Baseball (MLB). A right-handed batter, Williams played in Major League Baseball for the San Francisco Giants, Cleveland Indians, and Arizona Diamondbacks. He managed the Washington Nationals from 2014 to 2015, and was the third base coach for the San Diego Padres from 2022 to 2023.

A third baseman, abbreviated 3B, is the player in baseball or softball whose responsibility is to defend the area nearest to third base — the third of four bases a baserunner must touch in succession to score a run. In the scoring system used to record defensive plays, the third baseman is assigned the number 5.