O’Brien made himself into a reliable hitter with some power and a knack for getting on base. He constantly changed his batting stance during the hot and cold periods he experienced within each season, but his season totals were consistent. From 1984 to 1988 he hit between 16 and 23 home runs. He had a high of 92 RBI in 1985, but was generally in lineups where he had few RBI opportunities and wasn’t driven in by those behind him.
After the 1988 season, O’Brien was traded to Cleveland with Oddibe McDowell and Jerry Browne in the blockbuster deal that brought Julio Franco to Texas. He spent a year with the Indians before signing with Seattle, where batted just .237 over four seasons.
O’Brien was one of the best fielders in the league, as he showed by leading AL first basemen in assists in 1983 and 1987. When he started three double plays in a game on May 22, 1984, it tied the major-league record for first basemen.