In its simplest form, the running back position is about the balance between explosion and discipline. Discipline because you have to be true to the design of the offense and understand that every carry can't go for 40+ yards. Explosion because you can't afford to miss opportunities for 40+ yard plays when those opportunities arise.
There is no questioning South Carolina running back Mike Davis' explosion.
During the 2013 season, the 21-year-old back ran for 1,183 yards on 203 carries. He averaged 5.8 yards per attempt and scored 11 touchdowns while also contributing 38 receptions for 387 yards. In 12 games, Davis had a longest run of at least 20 yards on seven occasions. Five of those occasions saw him gain over 40 yards on a single rush attempt.
Speed can often be a very overrated aspect of a player's skill set. At the running back position in particular, it can prove to be fool's gold without other important traits. In college, Davis understood how to use his speed to be effective.
On this play, Davis doesn't have to create a route to the second level. The South Carolina offensive line creates a wide running lane up the middle of the defense for Davis to run straight through. He is immediately vaulted into space on the second-level, with the nearest unaccounted-for defender roughly eight yards away from the line of scrimmage.
Once on the second level, Davis has a wide open running lane down the middle of the defense. He would have a certain first down and a very good gain if he simply attacked this space. Instead, he turns his attention to the outside defender. He reads the positioning of the outside defender in relation to his receiver. That receiver isn't effectively blocking the defender, but he is in a good position to allow Davis to cut behind his back and towards the sideline.
Davis aggressively plants his feet and quickly turns his shoulders towards the sideline. He moves too quickly for the first defender to reverse his momentum and get outside of the receiver who was trying to block him. This releases Davis to the outside, but there is another defender with another receiver in position to cut him off before he can escape outside.
The outside receiver is doing an even worse job than the inside receiver. He clearly didn't expect Davis to cut as far back to the outside as he did.
Making this kind of decision can often backfire on a running back. It probably should have backfired on Davis, but his speed turned it into a good decision. When thinking of speed, the first thing that normally comes to mind is breakaway, straight-line speed that can be measured in a 40 time. However, speed isn't just one thing in the NFL.
A part of speed that is vitally important is acceleration. Acceleration is what allows Davis to escape to the sideline on this play. The outside defender was actually in a very good position to tackle Davis just a couple of yards after the first down marker. While he pivoted to get in a position to tackle Davis, the running back was already erasing his angle advantage. This forced the defender to drift further downfield and look to recover further down the sideline than he would have initially expected.
Davis' acceleration alone is very impressive, but it's even more impressive when you consider that he has already advanced onto the second level and made a hard cut to change direction.
Outrunning angles and getting around the edge of college defenses are things that Davis does consistently and comfortably. Being fast enough to outrun the defense and score from distance in college is slightly different from doing it in the NFL, where the athleticism of the defense sharply improves. In spite of that, Davis shouldn't have any issues translating to the next level.
Acceleration is Davis' greatest strength. It's also the most important aspect of speed in the NFL for a home-run hitting back. NFL defenses swarm to the football. Linebackers are as fast as they've ever been and defensive backs remain some of the most impressive athletes in professional sports when it comes to movement. If you have the top speed to run away from defenders on the second level, but you need 20 yards to get to that top speed, you will rarely ever get a chance to show off your ability to score from distance in the NFL.
Acceleration is also more important because of its value when running between the tackles. Running between the tackles requires quickly recognizing and quickly running through holes. Those holes don't generally stay open for a long time. Furthermore, if you are running off tackle or behind a group of blockers to the outside, you need to show patience behind the line of scrimmage before quickly hitting top speed to exploit space when it appears.
Davis has the acceleration to be effective in these areas. He is also a disciplined runner who understands how to find running lanes in different ways.