Danny Shelton, Malcom Brown Proving to Be Playmakers for Browns, Patriots

The first rule of defense is: Stop the run. 

The second rule of defense is: Those players who effectively stop the run are rarely discussed. 

Defensive tackles Danny Shelton and Malcom Brown, who were the top two defensive tackle prospects selected in April's NFL draft, weren't sexy first-round picks. Their impact, however, can prove to be immense even though they'll never receive the credit they deserve.

If their first preseason outings are any indication, both defensive tackles will deserve plenty of credit throughout their careers. 

Each player met his new team at very strange times.

The New England Patriots selected Brown with the 32nd overall pick. 

Bill Belichick's squad was coming off its fourth Super Bowl victory in 13 years. The organization was also embroiled in the Deflategate controversy. Plus, the team recently parted ways with veteran stalwart Vince Wilfork. 

For 11 seasons, Wilfork was the focal point of the Patriots defense. His immense size and strength allowed him to set the tone for the unit. But his play clearly started to slip during the team's Super Bowl run. 

In the playoffs, the Baltimore Ravens pushed around the Patriots' interior defense with ease, particularly early in the game. At that very moment, Wilfork's days in New England were numbered. Less than two months later, the organization declined a team option in the nose tackle's contract, and he became a free agent. 

With Wilfork's departure, a massive void opened up in the middle of the Patriots defense. Brown is expected to fill said void, and he did so admirably during his first preseason game against the Green Bay Packers. 

There were still issues with the run defense Thursday, but Brown was arguably the team's lone bright spot in this particular area, as Pro Football Focus' Steve Palazzolo noted: 

Brown shouldn't be mistaken for Wilfork, though. The rookie isn't nearly as big or powerful at the point of attack. Wilfork is one of the best the league has ever seen at demanding double-teams, which resulted in five Pro Bowl appearances. 

The first-year defender is more versatile and athletic than the veteran at this point in his career. Plus, Brown has already shown improvement early in the process. 

An inability to consistently and effectively hold up at the point of attack became the biggest concern regarding his skill set. The Texas product won at the line of scrimmage by capitalizing on an explosive first step and advanced hand technique. 

Against the Packers, however, Green Bay's offensive linemen had their hands full against Brown. 

NEPatriotsDraft.com's Mike Loyko provided an example of the young defensive tackle showing a quick first step, getting penetration, holding up at the point of attack and forcing a cutback into the teeth of the defense: 

There were certainly points during his collegiate career where Brown struggled to produce these types of plays. If the rookie continues to be this stout against the run on a consistent basis, though, he can serve as the team's starting 1-technique—the defensive tackle lined up on the outside shoulder of the center. 

Where Brown can ultimately help the Patriots defensive line the most is by injecting athleticism and overall talent into the rotation. 

As mentioned earlier, the defensive tackle is quick off the snap. He also tracks the ball well down the line of scrimmage. His lateral movement is something the Patriots lacked in recent seasons. 

Loyko provided another example of Brown's skill set. This time the defensive tackle disengaged from his block, made his read, scraped down the line of scrimmage and made the tackle after only a short gain: 

Again, Brown won't make anyone forget about Wilfork, particularly if he's asked to play nose tackle in a three-man front, but the potential is there to be a force against the run. 

Consistency remains the key, but the initial return is promising. 

In Cleveland, the Browns are desperate to stop the run and improve upon last year's 7-9 record. 

David Richard/Associated Press

Prior to Brown's selection at the end of the first round, Cleveland decided to address its 32nd-ranked run defense by choosing Shelton with the 12th overall pick. 

The organization feels that stopping the run remains the missing piece of the puzzle for the team to legitimately compete in its division and continue its overall improvement. 

A year ago, the Browns started 7-4 overall and were tied for first place in the AFC North. The team then completely fell apart at the end of the season and lost five straight contests.

A dichotomy existed between the talented secondary and the underperforming defensive front. As such, Cleveland struggled to slow opposing offenses when there were opportunities to claim more victories.

While a promising season steadily disintegrated into yet another last-place finish in the division, last year's first-round selections, cornerback Justin Gilbert and quarterback Johnny Manziel, provided nothing of substance to the team or its season. 

This year's first-round picks simply can't fall into the same state of limbo. It's not an option for the Browns after whiffing on so many opening-round choices after the franchise's return to the NFL. 

Shelton's selection can be viewed as a safe pick as a result. He's meant to be a major piece in finally stopping opposing ground games, but he wasn't necessarily projected as anything more than a two-down defender. There is nothing wrong with developing into a dominant run defender, though. 

The nose tackle combines gargantuan size (6'2" and 339 lbs on a good day), raw power and a relentless attitude to create a new identity along the Browns' defensive front. 

Shelton displays a never-ending motor that can ignite a spark within his teammates. Plays like the one below during the team's scrimmage (via ClevelandBrowns.com's Kevin Jones) send shock waves throughout the defense. 

Nose tackles aren't supposed to be running 15-20 yards downfield and laying out wide receivers along the sideline. If Shelton can show that type of hustle and determination, it puts his teammates on notice. 

His nonstop activity applies to stopping the run in the middle of the field as well. The rookie has all of the natural tools to develop into one of the league's best interior defenders, as noted by SI.com's Doug Farrar: 

The rookie defender made an instant impact during the team's initial preseason contest against the Washington Redskins. 

While the Redskins ran for 154 yards Thursday, the majority of the team's yardage came courtesy of outside runs. According to Jones, the Browns only surrendered 34 yards on 17 carries when Washington attempted to run between the tackles. 

Of course, Shelton wasn't the only reason behind the improved interior defense, but the former Washington Husky proved to be a constant presence even if he was only utilized in the team's base package when he lined up with the first-team defense. 

"It was a lot different compared to college as far as the play count and the play speed," Shelton said after the game, per ESPNCleveland.com's Tony Cartagena. "I just felt pretty comfortable and confident that I did my job and I did what I wanted to do.

"It wasn’t my best performance but I did some plays. I definitely want to go back and work on a couple of things and get better for the team."

Brown and Shelton are big, talented men who will not only get better throughout the rookie seasons from an individual perspective, but their teams will be better because they're in the lineup.

Patriots and Browns games will continue to go on, and few spectators will have any idea just how important these rookie defenders are to the success of their teams this fall. Why? Because stopping the run isn't sexy, even though it's vitally important. 

The final (and unwritten) rule of playing defense is: Good defensive tackles do the dirty work so their teammates can take all of the credit. 

Brent Sobleski covers the NFL draft for Bleacher Report. Follow him on Twitter @brentsobleski.