Since I have been a fan, there have been several players with huge expectations in the Red Sox minor league system. Some of these players, such as Mo Vaughn, Nomar Garciaparra, Trot Nixon, Jon Lester, and others meet those expectations. Others are not as fortunate.
Frankie Rodriguez was drafted in the second round of the 1990 draft and was a two-way talent, equally able to pitch and play shortstop. He actually played his first minor league season at shortstop, but then was moved to pitcher permanently. He was extremely talented as a young minor leaguer and was rated the #9 prospect in all of baseball by Baseball America prior to 1992. His ranking slipped a little in later years, but he was always in the Top 40 until he made the Majors.
He was a pretty good pitcher in the minor leagues too, keeping his strikeouts per nine innings right around seven to eight and an ERA below 4.00. Big things were expected of him. He was supposed to join the rotation behind Roger Clemens in 1995 and be a big-time starter from that point on.
He did join the Red Sox rotation for two starts in 1995 but was bombed. He then went to the bullpen for seven more games and did not fare much better. He was later traded to Minnesota in the trade that brought Rick Aguilera to Boston. He finished his Boston career at 0-2 with a 10.57 ERA and 14 strikeouts in 15.1 innings.
In Minnesota, Rodriguez continued to struggle. He was a starter for most of the next couple of years, but he never developed into the pitcher he was supposed to be. In 1996, he did win 13 games, but lost 14 and had an ERA of over 5.00. His strikeouts per nine innings were also dropping and his walk rate was increasing. Eventually, he was placed on waivers and picked up by Seattle, who used him almost exclusively as a reliever, but he never pitched as well as expected. He also pitched briefly for Cincinnati in 2001 but again was a bust. He was cut loose and retired at the age of 28.
In 2008, Rodriguez showed up in Newark with the Independent League Bears, but only pitched in nine games and had a 7.72 ERA.