He started out playing basketball in high school on a team that included future NBA player Kyle Anderson and switched sports despite his mother's concerns about the risks of injury in football.

Despite playing only two seasons of high school football at Paterson Catholic, he earned status as the top overall prospect in the state of New Jersey.

[2] As a senior, he helped lead his team to a perfect 11–0 record en route to the title.

He also established himself as a Division I prospect in basketball and received scholarship offers from Big East schools Providence and Seton Hall after he spearheaded a defense that notched five shutouts and yielded just 41 points on the year (3.7 points per game).

In track & field, Clemmings notched a top-throw of 12.90 meters (42 feet, 3 inches) in the shot put as a senior in 2009.

[7] Prior to the 2012 BBVA Compass Bowl, he was switched from defensive end to offensive tackle.

At the 2015 NFL Combine, Clemmings was the best of all offensive linemen with a vertical jump of 32.5 inches (0.83m) and a 4.54 20-yard shuttle.

Clemmings tied a franchise rookie record by starting all 16 games after the Vikings lost veteran starter Phil Loadholt at right tackle for the entire season due to an achilles injury.

After starting left tackle Matt Kalil was placed on injured reserve on September 21, 2016, Clemmings was announced as the starter for the rest of the season.