All eyes will be fixed on Heisman Trophy winners and No. 1-pick hopefuls Jameis Winston and Marcus Mariota as the NFL Combine begins Friday at Lucas Oil Stadium in Indianapolis.

More than 300 prospects will take on seven drills: the 40-yard dash, bench press, vertical jump, broad jump, three-cone drill, 20-yard shuttle, and the 60-yard shuttle.

Somewhat discounting their overall success in college, the league’s four-day evaluation of prospects entering May’s draft is typically the place where players either improve their stock for scouts and 32 prospective employers, but it can also be a major detriment.

With quarterbacks scheduled to work out on Saturday, Winston is presently unsure if he will participate in throwing drills for scouts and team executives, his coach George Whitfield told ESPN Wednesday. Whitfield also said the Florida State star’s agency will have some input into whether he throws.

Winston, who led the Seminoles to the national championship in 2013 but floundered in his second season and faces many questions about his behavior off the field, could instead ask scouts and the NFL’s 32 teams to watch him throw at his pro day, an event controlled more by the player and his representatives.

Mariota, the Oregon Ducks quarterback who threw for 4,454 yards and 42 touchdowns to four interceptions en route to the Heisman last season, will reportedly throw in the hopes of snagging the top overall selection from Winston.

In the past, a quarterback’s workout at the Combine has either dragged down his stock or had little effect. As Yahoo Sports pointed out, Carolina Panthers quarterback Cam Newton had a “so-so throwing performance” at the Combine in 2010, and still went first overall.

Andrew Luck and Robert Griffin III decided not to throw, and they went No. 1 and No. 2 overall, respectively in 2012.

As shown last year, if a prospect turns down the chance to wow scouts with his arm at the Combine, he better show up for his pro day.

At last year’s Combine, then-Louisville prospect Teddy Bridgewater chose not to throw, but followed up with a poor showing at his pro day, causing him to drop to the last pick in the first round and the loss of millions in guaranteed money.

Johnny Manziel, now in rehab after disastrous and checkered rookie year, displayed incredible athleticism at the Combine last year, nearly equaling Luck and Newton’s 40-yard dash times at 4.68 seconds and tied Bridgewater for fourth among quarterbacks in the broad jump.

Manziel decided not to throw, and his pro day became a nationally televised event. He looked far sharper than Bridgewater, and went No. 22 overall.

The Combine officially kicks off Friday, with tight ends, offensive lineman, and specialists getting in their workouts. But Saturday is when the prime offensive skills positions show their stuff, with quarterbacks, running backs, and wide receivers the focus of the day.

Though the workouts by Winston and Mariota will be the main events, UCLA’s Brett Hundley, Baylor’s Bryce Petty and Alabama’s Blake Sims are three quarterbacks that have a chance to be drafted in the first three or four rounds.

Over the last few years, running backs, no matter their talent, have fallen to the second round of the draft, but that could change if Wisconsin’s Melvin Gordon and Georgia’s Todd Gurley blow scouts away.

Gurley suffered a season-ending ACL tear in November, but he could still fall into the first round, according to mock drafts.

"You want to be out there with the guys," Gurley said to reporters Thursday. "You're happy for the guys that are out there competing, but at the end of the day you want to see yourself competing with those guys because that's what the combine is all about - going out there, doing the workouts, and showing the coaches what you can do."

Gordon finished second to Mariota in the Heisman vote after racking up 2,587 yards and 29 touchdowns for the Badgers last season, and he’ll be Gurley’s main competition at the Combine and the day of the draft.

Receiver’s to watch include Alabama’s Amari Cooper, who was third in the Heisman vote, West Virginia’s Kevin White, Oklahoma’s Dorial Green-Beckham, and Louisville’s DeVante Parker.

Cooper was second in the nation among receivers with 124 receptions for 1,727 yards and 16 touchdowns last year, nearly helping the Tide win the national title. White was sixth with 1,447 yards and 10 touchdowns off 109 catches.

Workout Schedule

Friday: Specialists, Offensive lineman, tight ends

Saturday: Quarterbacks, running backs, wide receivers

Sunday: Defensive lineman, linebackers

Monday: Defensive backs

TV Channel: NFL Network

Live Online Stream: A live stream is available at here