From the deadball era, Jesse Tannehill is one of the unsung pitchers from that time.

After appearing in five games for the Cincinnati Reds in 1894, he returned for good in 1897 with the Pittsburgh Pirates.  The southpaw played for Pittsburgh for five seasons, winning at least 20 Games in four of them.  In 1901, he "only" recorded the "W" 18 times, and he won the ERA Title (2.18).  He was also the National League leader in FIP twice as a Pirate. 

Tannehill later joined the Boston Americans, where he would have two 20-Win years.  After a stint with the Washington Senators and one more with the Reds, he retired in 1911 with 197 Wins against 117 Losses.

Bob Friend played most of his career with the Pittsburgh Pirates (1951-63), where he quietly had one of the better decades of the National League's Pitchers.

Friend cracked the Majors in 1951, but it was not until 1955 that he proved himself as a bona fide Starting Pitcher.  While his record was only 14-9, he led the NL in ERA (2.83) and bWAR for Pitchers (6.0).  Over the next three seasons, Friend was a workhorse leasing the league in Games Started in the first three years and Innings Pitched in the first two.  The three-time All-Star had his most decorated season in 1958, where he led the NL in Wins (22) and finished third for the Cy Young and sixth for the MVP.  Two years later, Friend was a large part of the Pirates’ surprise World Series win over the New York Yankees.

Friend played for Pittsburgh until 1965 and made brief stops with both New York teams before retiring in 1966.  He would have a losing record of 197-230, but was still highly regarded.

Despite his accomplishments, Friend was left off the Baseball Hall of Fame ballot when he was first eligible in 1972.

One of the most underrated players was Brian Giles, who played for three mediocre teams (Cleveland, Pittsburgh, and San Diego) and did not see as much love as he should have.

The Outfielder played his first four seasons (1995-98) as an Indian before he moved to the National League with Pittsburgh, and in his four full seasons as a Pirate, he never had less than 35 Home Runs, 95 RBIs, or a .298 Batting Average.  His On Base Percentage was over .400 in all of those seasons and received at least one MVP vote.  

The Pirates traded him to San Diego during the 2003 season, and while his power declined, his plate discipline remained strong, as he led the NL in Walks in 2005.  Giles played until 2009, and he retired with 1,897 Hits, 287 Home Runs, and a career Slash Line of .291/.400/.501.

The younger brother of Baseball Hall of Famer and New York Yankees legend Joe DiMaggio, Dom DiMaggio, was quite the player in his own right.