He went 10–2 with a 2.79 earned run average and led the Carolina League with 126 strikeouts with the Lynchburg Mets in his second professional season.

[2] Soon Allen emerged as the club's closer, earning eight saves by the end of the season and 69 total in his Mets career.

In May 1981, the Mets reached a deal to acquire Ellis Valentine from the Montreal Expos for Dan Norman and either Allen or Jeff Reardon.

[11] Following the '85 season, Allen was traded to the Chicago White Sox with Scott Bradley and Glenn Braxton for Ron Hassey, Matt Winters, Chris Alvarez and Eric Schmidt.

The White Sox converted him back to a starter, and he earned his first win of the season against Ron Guidry at Yankee Stadium on May 15.

Allen gave up only one earned run, four hits and two walks in seven innings for the first White Sox victory over Guidry at Yankee Stadium since August 13, 1980.

[14] In 2007, he joined the Rays' organization, working in their minor league system with his final stop as the pitching coach for the Durham Bulls.

[16] On May 26, 2016, Allen was booked into Hennepin County jail on suspicion of driving under the influence and suspended indefinitely by the Twins.

[17] After he completed a five-week outpatient treatment program at the Hazelden Betty Ford Foundation that the team had checked him in to, the Twins brought him back in early July.