Peter Robert O'Brien (born July 15, 1990) is an American professional baseball left fielder for the Pericos de Puebla of the Mexican League. He previously played in Major League Baseball (MLB) for the Arizona Diamondbacks and Miami Marlins. Amateur career O'Brien attended G. Holmes Braddock High School in Miami, Florida. He played for the school's baseball team, and transitioned to catcher during his senior year. Unselected in the 2008 MLB draft, O'Brien chose to enroll at Bethune–Cookman University, where he played college baseball for the Bethune–Cookman Wildcats team in the Mid-Eastern Athletic Conference (MEAC). In 2010, he was named MEAC player of the year. After the 2010 season, he played collegiate summer baseball with the Bourne Braves of the Cape Cod Baseball League. The Colorado Rockies selected O'Brien in the third round of the 2011 MLB draft, but he opted not to sign, and instead transferred to the University of Miami for his senior year, where he played for the Miami Hurricanes baseball team in the Atlantic Coast Conference (ACC). He was named All-ACC for the 2012 season. Professional career New York Yankees The New York Yankees selected O'Brien in the second round of the 2012 MLB draft, and O'Brien signed with the Yankees. O'Brien started his professional career with the Gulf Coast Yankees and after four games was promoted to the Staten Island Yankees. He finished his first season hitting .212/.256/.401 with 10 home runs and 34 runs batted in. O'Brien started the 2013 season with the Charleston RiverDogs. On June 21, 2013 he was promoted to the Tampa Yankees. After the 2013 season, he competed in the Arizona Fall League. O'Brien began the 2014 season with the Trenton Thunder of the Class AA Eastern League. Arizona Diamondbacks The Yankees traded O'Brien to the Arizona Diamondbacks for Martín Prado on July 31, 2014. The Diamondbacks assigned him to the Mobile BayBears of the Class AA Southern League. After the 2014 season, the Diamondbacks assigned O'Brien to the Arizona Fall League. The Diamondbacks assigned O'Brien to the Reno Aces of the Class AAA Pacific Coast League (PCL) in 2015, and converted him into an outfielder. On July 14, 2015, O'Brien participated in the Triple A Homerun Derby. He finished in second place with a total of 20 home runs. O'Brien made his major league debut on September 11, 2015, at Chase Field against the Los Angeles Dodgers. He went 1-for-1