But this season, Hadley saw an opportunity to play on the outside and took it.
"It's going well," Hadley said of the transition so far. "It can be frustrating at times ‘cause … [my first two seasons] you drill and train your mind to react as a Buck and when a play is called you think of your assignment as a Buck, and now you have to rewrite things in your mind and think as a Sam backer.
"So there's a lot of learning now going on for me. It gets a little frustrating at times, but all in all I feel good about it. I like the position. It's a fun position, it's exciting, so it's good."
Hadley actually had the opportunity to play Sam last year. Following his mission, Coach Mendenhall called him into his office and said the staff thought he could play any one of three positions: Sam linebacker, Buck linebacker or strong safety.
With Jameson Frazier and Jordan Pendleton playing Sam at the time, Hadley opted to play Buck and loved it.
Playing behind Brandon Ogletree, Hadley only started one game however. That came against Texas when Ogletree couldn't play due to injury, and Hadley recorded a team-high 12 tackles.
With Ogletree having returned for his senior season, but Pendleton and Frazier having graduated and thus vacating the Sam linebacker position, the timing for a position change worked out.
Sam linebacker became a good fit and simply gave Hadley more opportunity for playing time.
When asked if the switch give him a better chance of becoming a starter, Hadley said, "I believe so. Yeah, there's a good shot. Alani Fua and I are sharing reps at the one position now for Sam backer. He's a good player, so I'll have to compete and prove myself, but yeah, I'd like to be out there with the ones."
While he admitted that the switch in responsibilities has been difficult at times, playing Sam hasn't been completely foreign for Hadley.
"It's a lot like the position I played back in high school, Sam backer is, so there are a lot of things that I do in the Sam backer position that I feel good about, very natural."
Meanwhile, while he works on adjusting to his new position and making his bid to be the one new starter among the four first-string linebackers, Hadley is also awaiting the arrival of his younger brother Matt.
After a very successful prep career that included three Washington player of the year awards and a new Washington State record for career touchdowns , Matt will arrive at BYU in June in time for summer school and summer classes. Like Spencer, Matt played a wide variety of positions in high school, but is slated to play strong safety for the Cougars.
Naturally, big brother has given little brother some advice.
"I just tell him to run a lot, be in shape, because … I've never run like I have ‘til I got here."
Given Matt's high school football pedigree and the fact that some colleges recruited him to run track, he should be fine.
"He's a freak of nature," said Spencer.
The junior linebacker spoke quite glowingly about his younger brother.
"We played different positions [in high school], but even if we played the same position, he would have shattered anything I did."
Still, Spencer wasn't ready to say Matt is outright better than him.
"He's a great athlete," he replied with a grin when asked if Matt is better. "We're different, so I don't know if he's better, but he's a stud, that's for sure."
It's not uncommon for BYU athletes to play alongside a brother, but usually it's something they already experienced in high school or elsewhere. Matt, however, was only in the 8th grade when Spencer graduated from high school, so this will actually be the first time the two play organized football together.
"We never played together, so we're excited," said Spencer. "[I'm] excited to touch helmets with him."