In the minor leagues from 1963–69, he was 65–32 with a 3.00 ERA.[2]
Major league career
San Diego Padres
After debuting with the Padres in 1969, Roberts was sixth in the NL in walks per 9 innings (2.13) in 1970.[2] He went 14–17 for the last-place 1971 Padres, finishing second to the New York Mets' Tom Seaver with a 2.10 ERA.[2] He was sixth in the voting for the NL Cy Young Award, seventh in walks per 9 innings (2.04), ninth in innings pitched (269.7), tenth in complete games (14), and 24th in the voting for the NL MVP Award.[2] He held batters to a .191 batting average when runners were in scoring position.[2]
Houston Astros
Roberts was traded from the Padres to the Houston Astros for Derrel Thomas, Bill Greif, and Mark Schaeffer on December 3, 1971.[8] His being traded by the Padres was just prior to the Padres signing another Dave Roberts (see below), who joined the club in 1972. If this trade had not taken place, the Padres' roster would have featured two unrelated players named "Dave Roberts", making this among the few occasions where a team's roster featured two unrelated players with the same name.
In 1972, Roberts was 12–7 for the Astros.[2] In 1973, he recorded a career-best 17–11 record, setting a club record with a career-high six shutouts (second in the NL).[2] Roberts was the August 25, 1974 NL Player of the Week.[2] That season, he finished sixth in the NL in wins and sacrifice hits (12), seventh in games started (36), eighth in complete games (12), and tenth in ERA (2.85) and walks per nine innings (2.24).[2]
After pitching just two games for the Pirates in 1980, Roberts was purchased by the Seattle Mariners in April.[2] He pitched the rest of the season in Seattle, going 2–3.[2]
Following that season, Roberts became a free agent, and in January 1981 he was signed by the Mets.[2] He pitched just seven games for the Mets, going 0–3 with a 9.39 ERA, before being released in May.[2] In June, Roberts was signed as a free agent by the Giants, but never pitched for them in the majors.[2]
On January 9, 2009, Roberts died of lung cancer that he developed from asbestos exposure as a young man, at his home in Short Gap, West Virginia, at the age of 64.[5][12][13][14] According to his wife, Carol, he was exposed to carcinogenic chemicals while working for several offseasons as a boilermaker.[15] He is buried at Frostburg Memorial Cemetery, not far from Lefty Grove's grave.