King always thought Patricia would make a good coach. When King arrived in his office the day after games, Patricia greeted him and peppered him with questions about the game film he’d already devoured.

And yet, before he hired Patricia, King hesitated.

“Are you sure?’’ King asked. “Do you understand what you’re giving up?’’

The same question — “Are you sure?’’ — kept coming at Patricia, and he kept saying yes until he had reached a lofty level in his profession. In his seventh season with the Patriots and fifth as linebackers coach, Patricia has become perhaps Bill Belichick’s most trusted assistant coach. The Patriots will play 2010 without a coach holding the title of defensive coordinator, but no assistant will have more say about the defense than Patricia.

In 1996, Patricia was working as an engineer outside Syracuse, N.Y. A spot on the Dean’s List and a degree in aeronautical engineering from RPI is a golden ticket. Patricia’s starting salary was more than $50,000. Surely, it would soon swell to six figures. He could settle down, start a family, live a comfortable life.

None of that was what he wanted. Patricia wanted to coach football. He told King, yes.

In the following years, Patricia was dispatched to pick up recruits at the bus station in Troy, N.Y., fixed computers in Amherst, and ate via drive-through windows at 3 a.m. in Foxborough. He slept in offices and spent more time with film than with friends. The sacrifice was always worth it.

At RPI, Patricia didn’t play as a freshman and was still the backup as a sophomore when the starting center got hurt against St. Lawrence.

Patricia played every game the rest of his career. He was never particularly strong for an offensive lineman, not even at a Division 3 college. But he was smart and tough and he always made the right calls. He played guard when asked. Because Patricia couldn’t drive back defensive linemen, offensive line coach Ray Moran instructed him to cut-block on most running plays. His teammates called him “Scissors.’’

“He wasn’t the most talented kid even to play at this level,’’ King said. “I think that he understood that early on. It was an advantage for him to have to work that much harder. Nothing was easy.’’

“Matt was a grinder,’’ said Don Faulstick, Patricia’s offensive coordinator at RPI. “Lived in the weight room nonstop. That’s the great thing about Division 3. You don’t need much talent. You just have to want to be good.’’

Patricia couldn’t shake football. At Syracuse University, coach Paul Pasqualoni opened his practices in the spring and his offices in the summer to coaches who wanted to research football. One day when he could escape work, Patricia came by and introduced himself. Eventually, he decided he wanted a way back in. Football mattered more than security.

“From my personal standpoint, his engineering job wasn’t necessarily for him,’’ said Moran, now one of his closest friends. “It was for others.

“I think you graduate from RPI, you’re paying your way, you’re paying your loans, you’re supposed to be out there making big dollars and being part of big corporations. There’s that external pressure to say you’ve got to get into the ‘real world.’ ’’

Patricia started at RPI as a graduate assistant. He monitored study halls and oversaw weightlifting sessions. He broke down film and charted all of the information into a spreadsheet. He found more efficient methods for evaluating the team. He solved problems the way an engineer would.

In 1999, Faulstick had become the offensive coordinator at Amherst College. Faulstick told the head coach, E.J. Mills, that he knew a guy at RPI who could improve their film study.

Mills offered Patricia $8,000 a year as a graduate assistant. At the time, Patricia was married to his first wife. After Patricia accepted, Mills asked him, “What are you, nuts, dude?’’

While he studied for a master’s in education at UMass, Patricia filled numerous roles at Amherst. He coached the defensive line and coordinated the strength and conditioning program. His biggest contribution came in the film room. He told Mills there was a better way to record all their information. Before most coaches had heard of it, he had become expert in Xcel.

It came so easy to him. One day, Amherst got a new video system for scouting and recruiting. Faulstick thought, “How the hell are we going to do this?’’ When the coaches came into the office the next morning, it was finished. Patricia had set the whole thing up.

“Matty was a rocket scientist,’’ Mills said. “You kind of laugh at that, but that’s what he was.’’

“After a while,’’ Pasqualoni said, “I felt like I knew the guy even before I hired him.’’

Patricia assumed a familiar role.

“No job too small,’’ Pasqualoni said. “Long hours, short pay.’’

Patricia worked in quality control. Again, he revamped the video system.

His exuberance and versatility struck Pasqualoni. In the morning, Patricia could research trends across college football or spit out a statistical analysis faster than any other coach. In the afternoon, he could teach fundamentals on the practice field. There was nothing about football Patricia did not like.

“He was a very, very, high-energy, positive personality,’’ Pasqualoni said. “You knew what you were getting every single day. Very, very steady performer.’’

His time at Syracuse ended when Patricia landed his biggest break. He sent a résumé to the Patriots for a job as an offensive coaching assistant; basically, he would be a film guy. They interviewed him. Belichick gave him 24 hours to decide whether he wanted the job — he did.

In New England, Patricia put an inflatable mattress in his office. By 2004, Moran had left football and taken an analyst job that required him to wake up before dawn. He would call Patricia when he got up. Most times, Patricia would be grabbing fast food, his late-night meal before heading back to the Patriots offices.

“I don’t think he had an address for two years,’’ Mills said. “I think he lived in the office.’’

Patricia fit the profile of so many other Belichick assistants, which is to say he fit the profile of Belichick. He had played Division 3 football and knew the sport better than he could play it. He worked harder than he had to. He loved the game.

After Patricia’s first year in New England, Belichick let him help Dante Scarnecchia coach the offensive linemen. In 2006, Patricia finally landed a position that paid him more than he made after graduation. He became linebackers coach, the job he has held since. Before Belichick decided he would run the defense himself, Patricia appeared to be the leading candidate to replace Dean Pees as coordinator.

“Matt will definitely be a defensive coordinator, and he’ll build up to being a head coach someday,’’ said retired Patriots linebacker Junior Seau. “He’s a bright talent. He’ll be ready for it. I have all the confidence that Matt will be ready for it. He can step into anyone’s shoes.’’

For now, he is still linebackers coach, the same position every other Belichick defensive coordinator held before landing the job. Maybe next season, some 15 years after he walked away from rocket science, Patricia may find out that he is the Patriots defensive coordinator.

“I think he would just have a brilliant smile from ear to ear for about two hours,’’ Moran said. “And then he would realize, ‘My gosh I have a lot of work to do.’ ’’