Blackwell appeared in 44 games for the Red Sox in 1974, hitting .246 over 122 at-bats, collecting the first 30 hits of what turned out to be a 10-year career.
Never really a full-time player, the bulk of his MLB tenure was with the Chicago Cubs between 1978 and 1981, where he had his best year, in 1980 when he played in 103 games, hitting .272 with 87 hits and setting personal bests in pretty much every category because of the extra playing time.
After a couple of years with the Montreal Expos in 1982 and 1983, he retired, finishing up with a career .228 average, with 238 hits in 1044 at-bats in 426 games.