As we head into the 2015 NFL campaign, Bucky Brooks is identifying which teams have improved the most in particular position groupings since the end of last season. Today's focus: defensive lines.5) Cleveland BrownsIt is hard to believe the fielded the NFL's despite surrendering in 2014. The lack of available players along the defensive line robbed Mike Pettine of what he absolutely needs in his aggre sive scheme: active, big bodies to control the line of scrimmage. While the healthy returns of Phil Taylor and should shore up some of the i sues at the point of attack, it is the arrival of first-round pick that could help the ' D-line dominate opponents. The 6-foot-2, 339-pound rookie is an active defensive tackle with a unique combination of size, strength and athleticism that should create problems for opposing offenses. Shelton's presence in the middle should command double teams from foes, leading to one-on-one opportunities for the rest of the ' front-line players.The also added a pair of pa s rushers ( on the outside, on the inside) on Day 2 of the draft to further enhance a front that generated just 31 sacks a season ago (). Each player has flashed in the preseason (Cooper has three sacks in two games); they could make key contributions as situational playmakers as rookies. While it is tough to count on several first-year players to make an immediate impact, Cleveland's ultra-aggre sive scheme could allow the rookies to make their mark from Week 1.4 Benson Mayowa Jersey ) Houston TexansThe spectacular play of spearheaded the ' defense a season ago, but the 2014 Defensive Player of the Year needs more production from his supporting cast for the unit to spearhead a playoff run. Watt accounted for 20.5 of the ' 38 sacks while also delivering numerous splash plays against the run that helped the D get off the field in critical situations. While it is po sible that the perennial er could replicate that effort in 2015, Houston's defense could rise to prominence behind the arrival of and the return of . Granted, Wilfork is no longer the destructive force that terrorized opponents during his prime, but the big-bodied run stuffer still commands a double team at the point of attack and creates opportunities for active linebackers to flow freely to the ball. Given 's instincts, awarene s and athleticism, Wilfork's presence will allow the active 'backer to control the tackle-to-tackle box as the unit's designated playmaker.Meanwhile, Clowney is on track to return to the lineup following . Last year's No. 1 overall pick is a natural pa s rusher with extraordinary physical tools. Although critics question his motor and effort, there is no disputing his freakish athleticism and instincts as an edge rusher. If he can regain his pre-injury form, Clowney could give the the book-end Jamarco Jones Jersey rusher needed to dominate in a pa s-happy league.3) Miami DolphinsWhenever a defense adds arguably the most destructive defensive tackle in the NFL, the unit has an opportunity to field one of the best D-lines in the game. Thus, the deserve a spot on this list after adding , the crown jewel of free agency, this offseason. The sixth-year pro absolutely obliterates blocking schemes at the point of attack, creating chaos with his unique skills as a run stopper and pa s rusher. Suh has 36 career sacks in five seasons (including 8.5 in 2014) and creates one-on-one opportunities for edge rushers by commanding double teams on the inside. With and previously wreaking havoc off the edges without an All- Nigel Warrior Jersey Pro presence on the interior (the duo combined for 38 sacks over the past two seasons), the addition of Suh makes the ' pa s rush frightening.Miami also stands to benefit from the addition of to the rotation. The team's second-round pick is one of the most naturally gifted defensive tackles in the 2015 cla s, but questions about his work ethic and motor led to a slide down the charts on draft day. If he brings the effort and energy consistently, Phillips could join Suh to spark a much-improved defensive line.2) Washington RedskinsFor the to make a run at the NFC East title in 2015, the defense must find a way to control the trenches in a division loaded with elite offensive lines. To enhance their chances of holding the point, the team added in free agency. The 6-foot-3, 331-pounder affectionately known as "Pot Roast" is a dominant run stopper, exhibiting exceptional strength, power and balance controlling the line of scrimmage against double teams. Knighton's presence at the point of attack will allow linebackers to run and chase without obstruction, which should allow Washington to boast a top-10 run defense.On the edges, the arrivals of free agent and rookie should help the generate a consistent pa s rush in 2015. Galette's Ugo Amadi Jersey signing was viewed as controversial by some observers, due to his questionable off-field antics and falling out with the , but there is no disputing his ability to get to the quarterback. The sixth-year pro has recorded 22 sacks over the past two seasons, displaying outstanding quickne s and power off the edge. If he can stay out of trouble and quickly master the scheme, he should team with to give the one of the top rushing tandems in the NFC. Kerrigan thrived as the team's DPR (designated pa s rusher) without a sistance in 2014; he could take his game to another level with more one-on-one opportunities on the horizon.Smith could be the wild card for Washington this year. He has intriguing physical tools, but needs to polish his technique to become a disruptive force off the edge. If he can crack the lineup as a situational rusher by midseason, the ' defense could rank as one of the NFL's biggest surprises this year.1) Dallas CowboysFor all of the accolades hurled in the ' direction during their surprising run a season ago, the team captured the NFC East title despite fielding a defense that lacked star power along the front line. While Rod Marinelli's scheming and motivational tactics prompted a host of no-names to outplay opponents with energy and effort, the odds of duplicating that feat without upgrading personnel were slim at best. Thus explains the ' decision to gamble on a pair high-risk/high-reward edge rushers in and .Hardy, in particular, is a -caliber pa s rusher with a knack for getting to the quarterback. He posted 26 sacks over a two-year period (2012-13) before sitting out 15 games a season ago due to his misconduct off the field. Reports about his deplorable behavior off the field certainly raise legit Levi Lewis Jersey concerns about his character. Evaluating him strictly in a football sense, though, there are few questions about his rushing prowe s as an energetic playmaker. He overpowers blockers with his brute strength, yet also displays the agility to win with quickne s or fine se off the edge. With Hardy also playing with a feistine s that endears him to his teammates, the sixth-year pro could emerge as one of the leaders on the defense after serving .Gregory was universally viewed as a first-round talent for most of the pre-draft proce s, but then and plummeted his stock in April. Although he fell to the 60th overall pick, Gregory has already flashed big-time potential in Dallas and is impre sing evaluators with his Simeon Rice-like traits as a pa s rusher. If he quickly develops as a situational player and continues to grow as a young pa s rusher, the suddenly have a deep and talented rotation that will strike fear in the hearts of quarterbacks around the NFL.Follow Bucky Brooks on Twitter .