McDonald attended Bishop Amat Memorial High School, before accepting a football scholarship from the University of Southern California. He was the third-string quarterback as a freshman and the backup as a sophomore. He became the starter at quarterback as a junior and helped the team capture a share of the national championship in the 1978 season, while passing for 1,690 yards, 19 touchdowns and 7 interceptions. His only loss in his two years as a starter came against Arizona State University, after injuries to the Trojans' top two centers led to several fumbled snaps that opened the door for Sun Devil and future NFL quarterback Mark Malone to win 20-7. In 1979, he posted 2,223 passing yards, 18 touchdowns and 6 interceptions, while playing in a backfield with future Heisman Trophy winnersCharles White and Marcus Allen. He led the team to a 17-16 win against Ohio State University, after it entered the 1980 Rose Bowl as the number one ranked team in the nation. He was known for his poise and as a winner, finishing his college career with a 22-1-1 record, holding the NCAA mark for the lowest interception percentage in a career at 2.3% and the Pac-10 record of 143 straight passes without an interception.
Professional career
Cleveland Browns
McDonald was selected by the Cleveland Browns in the fourth round of the 1980 NFL Draft. He was a backup behind quarterback Brian Sipe in his first 4 seasons. He replaced Sipe in the last three games of the strike-shortened 1982 season, posting a 2-1 record and helping the team make the playoffs that had been expanded to 16 teams. He started in the first round of the playoffs, a 27-10 loss against the Oakland Raiders, after throwing for 281 yards and 2 touchdowns with no interceptions. Sipe won back the starting job the next season. In 1984, the Browns did not re-sign Sipe and gave the starting job to McDonald, who had a 5-11 record after enduring 53 sacks and registering 3,472 passing yards, 14 touchdowns and 23 interceptions. Against the New England Patriots, he had a career-high 320 passing yards on 23 out of 37 attempts and one touchdown. Against the New Orleans Saints, he tallied a career-high 75% completion percentage. Against the Houston Oilers, he completed 13 straight passes. In 1985, he was the third-string quarterback behind Gary Danielson and first round supplemental draft choiceBernie Kosar. He was waived on June 26, 1986. He left after passing for 5,269 yards, 24 touchdowns and 37 interceptions.
On July 16, 1986, he signed as a free agent with the Seattle Seahawks. He was released on August 26.
Dallas Cowboys
On November 4, 1986, he was signed by the Dallas Cowboys as a free agent to be the third-string quarterback, after starter Danny White was lost for the season with a broken right wrist he suffered during the 14-17 loss against the New York Giants. He reunited with pass offense coordinator Paul Hackett who was one of his coaches with the Trojans and the Browns. Mcdonald also became the first left hander quarterback to make the team in franchise history. In 1987, he beat rookie Kevin Sweeney for the third-string quarterback job, leading the team with a 92.0 quarterback rating in pre-season. After the players went on a strike on the third week of the season, those games were canceled and the NFL decided that the games would be played with replacement players. Sweeney was signed to be a part of the Dallas Cowboys replacement team, had success and was kept on the roster for the rest of the year along with McDonald. On August 23, 1988, he was released without playing a down in his time with the team.
