Statistically, McQuilken was one of the poorest passers in NFL history that actually received significant playing time; for his seven-year career, he had a 17.9 passer rating, second-worst ever among players with at least 200 attempts. He won only two of his seven starts as a Falcon, reaching his arguable nadir in a 1975 loss to the Minnesota Vikings, when McQuilken made 26 attempts with only five completions -- and five interceptions. (For his career, McQuilken would throw 29 picks against just four touchdowns, also one of the worst ratios in NFL history.) In 1978, he went to the Washington Redskins as Joe Theismann's backup, appearing in just three games in 1979.
Out of football for three years, McQuilken, still popular in the Washington area, joined the Washington Federals of the United States Football League in their 1983 inaugural season and emerged as their opening-day starter. Ultimately he would complete 188-for-334 passes for 1,912 yards, seven touchdowns, and 14 interceptions for the season. However, the Feds would finish just 4-14 in front of small crowds, and the 32-year-old McQuilken retired.