O'Brien was a solid defensive catcher and a modest right-handed batter. He is best remembered for pioneering the hockey-style catcher's mask, which he created while with the Blue Jays. During his tenure with the Braves, O'Brien was notable for being the personal catcher for Baseball Hall of Fame pitcher Greg Maddux.
In his senior year, O'Brien set school records, hitting 25 home runs and driving in 116 runs as the Shockers reached the finals of the 1982 College World Series. The Oakland Athletics drafted O'Brien in the fifth round of the 1982 MLB draft, and signed him. O'Brien made his MLB debut with the Athletics on June 2, 1985.
O'Brien agreed to a $370,000 contract for the 1992 season.[5] He was granted free agency for the 1993 season, and he signed with the Atlanta Braves on a two-year contract worth $1.1 million.[6] He was a member of the 1995 World Series champions, and hit a key home run for the Braves during the 1995 National League Championship Series.[7]
After the 1995 season, O'Brien became a free agent and signed with the Toronto Blue Jays on a two-year contract. He signed with the Chicago White Sox for the 1998 season in order to share the catching position with Chad Kreuter,[8] but was traded to the Anaheim Angels for minor leaguers Brian Tokarse and Jason Stockstill in July 1998.[9] The Angels released O'Brien on August 6, 1999, replacing him with Benjie Molina.[10] Now 40, O'Brien signed with the Montreal Expos for the 2000 season, but his success at preventing stolen bases had diminished.[11] The Expos released O'Brien on June 22, 2000.[12]
Over the course of his career, O'Brien caught eleven different Cy Young Award winners: Frank Viola, Dwight Gooden, Bret Saberhagen, David Cone, Greg Maddux, Tom Glavine, John Smoltz, Pat Hentgen, Roger Clemens, Chris Carpenter and Jack McDowell.[1] However, he only caught three of these pitchers during Cy Young seasons—Clemens, Hentgen & Maddux. During Maddux's 1994 and 1995 seasons when he posted ERA's of 1.56 and 1.63 respectively, O'Brien generally served as Maddux's personal catcher.[13] O'Brien later testified at Clemens' perjury trial.[14] He is one of the few players to play both major league Canadian teams, the Toronto Blue Jays and the Montreal Expos.[15]
After getting hit in his mask by two consecutive foul-tip balls in a game, O'Brien had the idea for a new catcher's mask while watching a hockey game. He then worked with Van Velden Mask Inc., of Hamilton, Ontario, Canada, to develop his idea. The new design, called the "All-Star MVP", was approved in 1996 by Major League Baseball.[1][16]