The Buffalo Bills have a five-time NFL MVP finalist as their starting quarterback, but even Josh Allen has been overshadowed a bit this summer.While first-year head coach Joe Brady and new wide receiver addition DJ Moore are garnering their share of attention during the first two weeks of Bills' training camp, the main attraction has been Jim Leonhard's defense.Unsurprisingly, Sports Illustrated national writer Matt Verderame chose to lead with the defense when recapping his visit to St. John Fisher University.After Buffalo's defense failed to finish the job in any of the Bills' last five playoff losses, defensive-minded head coach Sean McDermott and his bend-but-don't-break scheme were shown the door.Bills new head coach Joe Brady talks with new defensive coordinator Jim Leonhard during the opening day of Buffalo Bills training camp at St. John Fisher University Wednesday, July 29, 2026 in Pittsford. | USA TODAY Network via Reuters ConnectReinforced by the promotion of offensive coordinator Joe Brady to head coach, Bills' brass apparently saw the defense as the primary obstacle standing in the way of a Super Bowl appearance. Brady tabbed Leonhard, a former NFL safety, to overhaul the defense, and the early reviews have been nothing short of encouraging.Going up against a new scheme, particularly one devised by a mad scientist with 10 years of NFL playing experience to his credit, has been a serious challenge for the Bills' offense, especially Allen and wide receiver Khalil Shakir, during training camp practices. "It's definitely not easy," said Allen after the summer's final St. John Fisher University practice. "The pressure looks that they can show you and the actual pressures that come with those looks are two different pictures. When you're looking at the pre-snap look compared to when I get to my back foot, the amount of change in that defense is pretty crazy."Bills quarterback Josh Allen throws downfield during the final day of Buffalo Bills training camp at St. John Fisher University Friday, August 7, 2026 in Pittsford. | USA TODAY Network via Reuters ConnectJim Leonhard's 3-4 front keeps opponents guessingAs opposed to McDermott's 4-3 base defense, Leonhard is employing a 3-4 front that features three down lineman and two stand-up edge rushers classified as outside linebackers.After practicing against the same defense for the first eight seasons of his career, Allen is seeing plenty of foreign looks that need be deciphered before he releases the football."You really have to understand what type of coverages that they're playing. Are they matching? Are they dropping off? Are they playing man? Like all these decisions happen within a couple seconds," said Allen.Shakir has found himself straining to correctly identify the pre-snap looks, too.Bills wide receiver Khalil Shakir gets ready to catch the pass during Bills Training Camp at St. John Fisher University in Pittsford on Aug. 3 2026. | USA TODAY Network via Reuters Connect"Honestly, this year in practice, it's been kind of like, wait, what was that? Like, what are they doing now? A few times I've come off the field, like, did they go this cover to that cover?" said Shakir on Eric Wood's Centered On Buffalo Podcast. "He's very good at just switching things up and giving us a new look every single time. Doing that consistently, and at the level that they're doing it at, is amazing to see, but confuses the heck out of us."The way Leonhard has been able to use the Bills' pieces up front adds another layer for Allen to solve."You got to get the ball out because now we got Bradley Chub, Greg Rousseau, Ed Oliver, and some one-on-one looks that I think it's going to make it really hard for opposing offenses to handle that," said Allen. "We got some studs up front, so you got to let your guys be guys, and they're having a really good camp right now."Shakir suggests that the practice battles will better prepare the Bills' offense for what they'll face from opponents throughout the season. It's worth noting that Leonhard was the defensive pass game coordinator for the Denver Broncos when they eliminated Buffalo this past January."It's good for us to see that stuff, especially early on. That's going to help when the season comes and teams are throwing different looks at us," said Shakir.Jan 17, 2026; Denver, CO, USA; Denver Broncos defensive tackle Malcolm Roach (97) tackles Buffalo Bills quarterback Josh Allen (17) during the second quarter of an AFC Divisional Round playoff game | IMAGN IMAGES via Reuters Connect— Sign up for OnSI’s Free Buffalo Bills Newsletter —Add us as a preferred source on GoogleFollow