Boston College played a pretty demanding schedule in the ACC with a "ball control" offense that couldn't control the ball (or score) and still managed to finish third in S&P defense behind star-loaded Alabama and Michigan units.
Yet while those programs had top rated recruits and depth all over, Boston College defensive coordinator Don Brown was working with a cast of 0-3 star players the Eagles didn't have to fight with major programs over. Unlike similarly unheralded units like Temple, this squad also ranged in experience with the DL consisting largely of upperclassmen while the defensive backfield was often filled with sophomores and freshmen.
The Eagles were very solid across the board ranking 2nd in rushing S&P and 15th in passing, 11th in the country on standard downs and 1st in all of the land at defending passing downs. They were largely without major weaknesses at any level of the defense but instead had players who's strengths were easily blended together.
Here's how it all came together:
Attacking up front
Four down defensive structures like the 4-3 that Boston College plays are often cautious in the defensive backfield these days with linebackers and defensive backs reading their coverage assignments for keys before rushing into action to join the melee in the trenches.
You can see on this snap against Florida State how cautious and aware the Eagle backfield is about play-action (or run/pass options for that matter) as they are playing man coverage and always looking to maintain leverage to match-up in coverage or make pass drops:
The result of this style, in which the linebackers and down safeties aren't rushing into battle at the line of scrimmage, is that the DL has to bear more responsibility for winning the point of attack. For a team who's DL doesn't include any 4/5 star bluechip recruits that can be a tall order.
However, the 2015 Eagle DL not only controlled the line of scrimmage for their team all season but also regularly went on the offense and dished out punishment to opposing protection schemes, as evidenced by their #1 finish in defensing passing downs.
Let's start by looking at their run defense, this snap against Florida State reveals a lot of what was excellent about this Boston College front:
This is an Over front from Boston College, they were a multiple front defense but they tended to play a lot of Over which is a style that puts a lot on the 3-technique defensive tackle to be able to control the strongside of a opposing formation. What's interesting about that choice from the Eagles is that it was actually their nose tackle, Connor Wujciak, who was their best player, although defensive tackle Truman Gutapfel was no slouch himself.
On this play the Seminoles failed to understand this and ran inside zone to the weakside, at Wucjiak and weakside defensive end Harold Landry, with double teams on both of the Eagle defensive tackles.
As you'll notice, not only did these double teams fail to clear Wucjiak or Gutapfel off the ball but the Eagles actually managed to squeeze closed any of Dalvin Cook's potential running lanes. Inside zone is all about opening creases between the tackles by blowing open holes with double teams but they just couldn't make that happen here. What's more, Landry beats the right tackle with an inside move off the ball and is in the backfield immediately, forcing Cook to pick a way through the pile of bodies up the middle.
Harold Landry began the year behind Kevin Kavalec on the depth chart but the elder defensive end was knocked out of the game by a vicious crack back block by the 'Noles, a big play that proved to backfire on FSU. Landry ended up amassing 15.5 tackles for loss and 4.5 sacks on the year and his pairing on the weakside with Connor Wujciak made for a nasty identity.
The Eagles were very clever about attacking opposing teams' protections with these players and as a result of making great use of Wucjiak and Gutapfel's ability to stunt and move around after the snap, they rarely had to bring more than four or five rushers to get real pressure on opponents.
Perhaps their most effective tool was the trap-2 Fire Zone, a blitz scheme that is becoming immensely popular across the college football landscape. With the typical three-deep, three-under Fire Zone defenses have often found themselves vulnerable to offenses that were good at spacing out the underneath defenders and getting receivers open on horizontal stretch plays underneath, or at picking on the corners playing on islands on the outside.
But this blitz scheme is a two-deep/four-under structure that has two deep safeties sitting on top of any attempt by the QB to make the defense pay with a quick throw down the sideline and corners or LBs sitting in the flats to stop any hot routes on the outside.
One of the benefits of playing base four down defense in which the DL are asked to specialize in the finer points of trench warfare is that time that other programs spend teaching players how to make pass drops can be spent entirely on learning to use their hands to help them stunt and beat blocks. The Eagles' defense makes use of a ton of different slants and stunts and their DL are very effective at using their hands to keep OL off of them and give them free movement to the ball.
In particular, the ability of Gutapfel and Wucjiak to get over multiple gaps on the pass rush and occupy blockers while ends or linebackers dash through gaps was absolutely devastating to opposing protection schemes. When you can regularly get effective pressure while sending four or five rushers and playing either two-deep or single-deep safety coverages it becomes very difficult to attack you on passing downs.
Calculated aggressiveness on the back end
The ability to bring pressure with multiple coverage schemes on the back end is a large part of what makes the Eagles so fearsome in pass defense. If you aren't sure whether you are facing a two-deep or one-deep coverage it's hard to have hot routes and blitz-beaters ready to go that can pinpoint the weak spots in coverage.
That said, Boston College also has good personnel in the defensive backfield that don't make it any easier for opposing offenses.
The linebackers are play-makers, who really know how to take advantage of the opportunities created by the superior DL playing in front of them. Middle linebacker Steven Daniels had a brilliant season with 16 tackles for loss and six sacks while also leading the team in tackles and strongside linebacker Matt Milano added another six sacks and 16 tackles for loss blitzing the edge in their nickel package.
Their secondary thrived as well thanks to the versatility of safeties Justin Simmons and John Johnson, both labeled as cornerbacks coming out of high school and now both versatile safeties. Simmons is good in man coverage and regularly plays down over slot receivers in their cover 1 schemes.
When the Eagles play two-deep they can both cover a lot of ground on the back end, which helps the two-deep fire zones work effectively. They combined for eight interceptions on the year and five pass break-ups, so they got their hands on quite a few passes and usually held on. At corner the Eagles have a few long, 6'0"+ corners that are good in press-man coverage as well as 5'11" left cornerback Kamrin Moore who was often left isolated in coverage when the Eagles wanted to roll coverage.
The preponderance of press-man coverage played on the back-end really paired effectively with the front's ability to get effective pressure with their stunts and blitzes. When a QB is looking at tighter coverage that makes him hesitate then a good pass-rush can become a great one. The ability of their safeties to play deep coverage is probably the strongest point of their team though, as seen on this two-deep blitz:
Golson actually had about four or five seconds to make a throw here and he also had Justin Simmons facing two deep receivers running into his zone in the wide open spaces to the field, but Simmons' positioning and range made it too risky. Golson held the ball, looked down, and then he was finished.
Simmons' versatility and range on the back end, either playing outstanding deep zone like above or else playing man coverage on a slot, was probably undervalued in his 2nd team All-ACC recognition.
With a quick LB corps, safeties that can play multiple roles, and effective DL anchored by highly skilled tackles all of the schematics and skill sets on the Eagles' defense were able to pull together to form a dominant unit. They were hard to move the ball against on normal downs and then pure murder on 3rd and long. Too bad about that offense.