Swan's best season came in 1978 when he posted a 9–6 win–loss record and led the National League with an earned run average of 2.43.

At age 17, was picked in the 23rd round of the 1968 Major League Baseball draft by the St. Louis Cardinals.

[2] For his efforts, he was named to the All-Tournament Team but Arizona State lost to the University of Southern California in the championship game.

In the Mets' last good season of the decade, Swan was the fifth starter and posted statistics slightly below the league average with a 3.54 ERA and a 6–9 record.

In 1978, the Mets struggled to a 66–96 record but Swan started the season with a five-hit complete game shutout, the third of his career.

After losing his next four decisions, Swan was placed on the disabled list in mid-July with what turned out to be a torn rotator cuff.

When play resumed, Swan was back on the disabled list and made only one more start the rest of the season.

After missing almost all of 1981 with a rotator cuff injury and the aforementioned broken rib[1] and baseball strike, Swan returned healthy in 1982 and finished second to Joe Morgan for the N.L.

Swan even hit the only home run of his career on August 4, although the event was overshadowed by his teammate Joel Youngblood becoming the only player in major league history to play for two teams in two cities in one day.

In 1984, while the Mets were finally ending years of futility, Swan managed only ten awful relief appearances before being released on May 9.

After numerous injuries forced the end of his career, Swan used the medical knowledge he obtained from his ordeals to invest himself in the technique known as Rolfing.