He had a record of 6-2 in 1976 with the Advanced A level Lakeland Flying Tigers in the Florida State League and an earned run average of 2.22.

Underwood split the 1977 season at different levels in the minors, spending the first half of the year at Montgomery in the AA Southern League, where he had a record of 9-2 and an ERA of 3.38 with 64 strikeouts in 104 innings of work.

[5] Underwood also started against the Chicago White Sox on the famed Disco Demolition Night at Comiskey Park, going 7+1⁄3 innings and giving up just one run in what was supposed to be game 1 of a doubleheader.

In 1982, Underwood was back in the minor leagues at Evansville, where he was used exclusively as a starting pitcher, and had a record of 9-8 with an ERA of 3.98, with 90 strikeouts in 165 innings.

His final major league appearance was on June 21, 1983, when he gave up five runs in two innings as part of a 10-3 loss to the Milwaukee Brewers.

[1] Underwood pitched in 1984 for the Rochester Red Wings, the Orioles' AAA affiliate, and had an 0-2 record and an ERA of 9.00 in three appearances in relief.