Mark Richard Vlasic (born October 25, 1963) is an American former professional football player who was a quarterback for six seasons in the National Football League (NFL). During this time, he played for the San Diego Chargers, Kansas City Chiefs and Tampa Bay Buccaneers. Over the course of his career, he played in 15 games, completed 75 of 142 passes for 762 yards, threw four touchdowns and five interceptions, and finished his career with a passer rating of 63.2.

Vlasic played college football for the Iowa Hawkeyes and was selected in the fourth round of the 1987 NFL draft by the San Diego Chargers. He was a backup for Dan Fouts during his first season, then started two games the following year. After not seeing playing time in 1989, Vlasic started the season opener in 1990, his last year with San Diego. He played for two seasons with Kansas City and one with Tampa Bay, but was released in 1994, having not had actual playing time since 1991.

Vlasic was born in Rochester, Pennsylvania. He attended Center High School and was a standout in football and basketball there. He was the starting quarterback for Center in his junior year, throwing for 777 yards in the first eight games of the season. In his junior year of basketball, Vlasic was a starter, in one game scoring 23 points and 11 rebounds with a bad back. He continued to play football and basketball during his senior year, with performances that included a 36-point effort against Las Vegas Western High School, making 18 of 20 shots. As a result of his high school career, Vlasic was inducted into the Beaver County Sports Hall of Fame in 1999.

After graduating from high school, Vlasic played college football at the University of Iowa. For four years, he served as a backup to Chuck Long, now a member of the College Football Hall of Fame. During his junior year, as the backup quarterback, he also served as the holder for field goal kicks. After placekicker Rob Houghtlin won a 12–10 game against the University of Michigan thanks to a last second field goal, a mob tore down the goalpost, which injured four fans including Vlasic, who was at the bottom of a pile of fans.

The following season Vlasic, now a fifth-year senior, became the starter, as Long graduated. Although he was taking over for the Heisman Trophy runner-up, his strong arm was complimented, albeit backhandedly, by coach Hayden Fry, who said, "He's got a stronger arm than Long, and he proves it every day by overthrowing his receivers." In Vlasic's first game as starter, he threw for 288 yards in a 43–7 win against Iowa State University, a game that made Hayden Fry the most victorious coach in Iowa football history. After two more victories, Vlasic went down with a separated shoulder, returning to the lineup after freshmen Dan McGwire and Tom Poholsky took over the starting role.

In a late October game against Northwestern, Vlasic threw a 93-yard touchdown pass to Quinn Early, the longest in Iowa history, in a 27–20 victory against Northwestern University. Despite his injury causing him to serve as a backup most of the season, he was given the start for the 1986 Holiday Bowl against San Diego State University. In the Holiday Bowl, Vlasic completed 15 of 28 passes 222 yards and ran for a touchdown as Iowa won, 39–38.

Vlasic was selected by the San Diego Chargers in the fourth round of the 1987 NFL draft with the 88th overall pick. Chargers coach Al Saunders chose Vlasic because he wanted to find a young quarterback to observe and succeed Dan Fouts. He signed with the team in late July, and spent the preseason competing with Rick Neuheisel, Tom Flick, and others for the backup quarterback job. While he performed well in the preseason, the Chargers were looking to have him sit out a year so he could learn the ins-and-outs or pro football. After Flick was cut and Mark Herrmann named the primary backup, Vlasic beat out Neuheisel for the final quarterback spot on the Chargers' roster, though Neuheisel would rejoin the team later that season due to the strike. Despite making the roster, Vlasic spent most of the season after the players' strike on the team's inactive list. However, when Fouts was scratched from a December game against the Denver Broncos due to a shoulder injury, Vlasic was called up to be Herrman's backup. He made his professional debut on December 27, 1987, playing the final 5:29 of the game. He completed three of six passes for eight yards, was sacked, and threw an interception in the Chargers' 24–0 loss against Denver.

Before the 1988 San Diego Chargers season began, Dan Fouts chose to retire from the game after 15 seasons, leaving Vlasic as the main backup to starter Mark Herrmann, and as a result the Chargers began trying to trade for an experienced quarterback. The Chargers also signed Mark Malone and Babe Laufenberg to compete for the starting job, and traded Herrmann to the Indianapolis Colts. After months of training and the 1988 preseason, Vlasic began the season as the third-string quarterback behind Malone and Laufenberg, who won the starting job. In November, after Laufenberg was injured, the Chargers decided to make Vlasic the starter instead of Malone due to the latter's ineffectiveness, as well as a six-game losing streak. He made his season debut against the Atlanta Falcons on November 13, and threw for 190 yards in a 10–7 victory. As a result of his performance, coach Al Saunders said that Vlasic would have the starting job for the rest of the season. Vlasic's second start came against the Los Angeles Rams where he threw for 80 yards and a touchdown. However, he suffered torn ligaments in his left knee late in the third quarter, and was lost for the season. He finished the season with 25 of 52 passes completed and a passer rating of 54.2.