FOXBOROUGH, Mass. -- New England Patriots quarterback Tom Brady has often cited how fortunate he's been to play in one offensive system over his NFL career, which aided in his initial growth from long-shot 2000 sixth-round draft pick to what he is today.

Others aren't as fortunate, and one timely example is new Patriots linebacker Shea McClellin, who agreed to a three-year deal with the club earlier this week that is in the process of being finalized.

I spent part of the past two days watching some of McClellin's tape from the first four years of his career, with the hope of gaining a better understanding of what his best fit with the Patriots might be. Here's the key snapshot since he was selected by the Chicago Bears in the first round of the 2012 draft (19th overall).

2012

Defensive coordinator: Rod Marinelli

Scheme: 4-3

Role: Sub-rushing defensive end

2013

Defensive coordinator: Mel Tucker

Scheme: 4-3

Role: Starting defensive end

2014

Defensive coordinator: Tucker

Scheme: 4-3

Role: Linebacker

2015

Defensive coordinator: Vic Fangio

Scheme: 3-4

Role: Inside linebacker

Every time a player has to learn a new scheme, and in the case of McClellin a new position two years into his career, it can stunt development. In his rookie year, McClellin was used mostly on third down as a designated pass-rusher. The first regular-season snap he played, for example, he aligned with a wide split and then twisted inside on Colts left tackle Anthony Castonzo. Later in that game, he executed an effective spin move on Castonzo.

But first-round draft picks usually aren't selected to be designated pass-rushers, and in McClellin's second season, he was elevated to a starting defensive end role under Mel Tucker, the new coordinator. McClellin struggled in the tape I watched, a bit undersized and under-powered to play that role on a consistent basis.

In the third year, McClellin switched his jersey number from 99 to 50, signifying a position change from end to linebacker in the 4-3. In the tape I watched, he was on the field for early downs before coming off in obvious passing situations. McClellin dropped some weight with that transition, and showed he could open his hips and fluidly drop into coverage, which is usually the biggest challenge for defensive ends moving to linebacker. Occasionally, he would play on the end of the line of scrimmage in a two-point stance and rush.

Finally, the 2015 season saw more change, with McClellin playing full-time at one of the inside linebacker spots in new coordinator Vic Fangio's 3-4. This required him to play more sideline-to-sideline and also downhill in the running game, where he didn't shy away from contact (e.g. taking on Packers fullback John Kuhn and shedding his block) and was a willing tackler. He also appeared to be a point person for the overall communication within the front seven; several times, I watched him re-position defenders, which seemed to indicate his command of the overall scheme in not just knowing his role but also the roles of other players.

Overall, I didn't see too many impact plays.

Where he fits in New England: Projecting where McClellin fits in New England, his situation reminded me a little bit of Akeem Ayers' from 2014. Ayers, who got caught in a scheme change in Tennessee, was a bit undersized to be a full-time defensive end in the Patriots' scheme, so in the base defense, he was more likely to be an off-the-line linebacker. But in the various sub packages the Patriots ran, Ayers could also find himself in a pass-rushing/niche role, depending on the game plan that week. I think McClellin could do something similar as his pass-rushing background makes him different than a pure off-the-line linebacker (e.g. Jerod Mayo). One key will be what weight McClellin plays, as his current weight (245) is undersized to do that. If he stays at 245, that would indicate he's more of a pure backup option to Jamie Collins as an off-the-line linebacker. If he adds some weight to get closer to the 260-pound mark he was at when entering the NFL, that could push him closer to an Ayers-type role. He's a versatile piece in that regard, as noted by ESPN NFL analyst Louis Riddick. McClellin also should factor into the special-teams mix in New England (e.g. he played on the punt rush and kickoff coverage teams in the tape I watched).