It was nothing personal, but philosophical differences between Damon Harrison and Matt Patricia ultimately drove Harrison out of Detroit.

Harrison, who was released by the Lions this offseason, said his discomfort in Patricia's defense led to him requesting a trade prior to last season and eventually parting ways with the team after a disappointing year. It was a partnership that sounded doomed from the start.

"When I got there last year it was fresh, it was new and I was a bit angry. And to be completely honest with you, I didn’t want to go to Detroit because of some things that I heard from some guys in the past and some guys who were there," Harrison said on the Green Light Podcast with former NFL defensive end Chris Long. "When I got the call that that’s where I was traded, I didn’t answer the phone for a couple hours. Bob Quinn was calling me and I didn’t pick up the phone because I was trying to figure out a way to get out of it.

"When I got there I didn’t know anything about the scheme. I was a nose tackle my entire career, 1-technique, shade, zero, some 2-wide. I get there and it’s 2-, 3- techniques. Now for me, in my career, the most frightening thing was playing 3-technique because of how far back the guards would sit."

When Harrison found out he'd be playing mostly 3-technique in Patricia's defense, he said "I tried to get out of it."

"We had some conversations about not doing it anymore, and they kind of incorporated some of that zero nose, shade to kind of fit my play style. But it was something that I wasn’t comfortable with. I had some success doing it, but this past year I think it kind of came back to bite me in the ass. I wasn’t prepared for the season mentally. I came into camp in shape, but during the first three weeks of camp I think I kind of worked myself out of shape because I wasn’t doing anything.

"That was a time where, to be honest with you, we were trying to facilitate a trade. I was hell-bent on getting out of there. It’s nothing against the people of Detroit, the city or anything like that. I’ll forever love the city of Detroit. But I just had to go try to put myself in a situation where I saw myself there for two or three years to end my career, and I just didn’t see myself in Detroit for that long."

Harrison excelled in his first season with the Lions, keying the team's defensive turnaround in the second half of the year. The club rewarded him with a one-year, $11 million extension to keep him in Detroit through 2021. But Harrison's play slipped in 2020 as he battled injuries and general frustration with the defensive scheme. He had more tackles and tackles for loss in 10 games with the Lions in 2019 than he did in 15 games in 2020.

When Long mentioned he had similar "X's and O's" disagreements with Patricia during his one season the Patriots, Harrison replied, "You know how he is."

"It was tough trying to get adjusted to a new team, new coach, new training staff," Harrison said. "You have to learn everybody, everybody has to learn you and I think it just got out of hand early on and I was trying to do too much to catch back up and my body suffered for it. I wanted to get back to the 2-wide, shade, 1-technique to where I can be the best player and get the best out of me."

Harrison wasn't alone in his struggles in 2020. Detroit's defense was bad across the board, nearly the worst in franchise history. Harrison said the defensive line had a hard time executing one play in particular, but the coaches insisted on calling it.

"Matt Patricia and I, as well as our defensive line coach and assistant defensive line coach and defensive coordinator, we spent a lot of time last season going over the block because it was a block that was troubling our entire defensive line. ... He’s showing us the drill, "Okay, when he turns like this to go, you push him, put your hand here,' and I’m like, 'No, he’s not going that flat," Harrison said.

The sticking point, said Harrison, was trying to attack an offensive lineman who was moving laterally instead of one moving forward.

"I’ve been taught to attack who’s trying to block me. Fight pressure with pressure. If the center’s going away and the guard’s coming, I’m going to attack the guard. That’s just the way I was taught and that wasn’t the way that we played it in Coach Patricia’s defense," he said.

Harrison also discussed his decision to skip mandatory minicamp last offseason, which he said wasn't related to his pursuit of a new deal. His wife, who lives in Texas with their family, was ill at the time. And when Harrison did report for training camp, he said "mentally I was just out of it, man."

"I couldn’t focus on football. I was too busy trying to get caught back up with everything. It was a rough training camp for me, the roughest training camp of my career. I just spent a lot of time pondering my future. My wife and my family was back in Texas, my wife was having issues with a gallstone and I was in Detroit. We live in Texas where we don’t have any family, so at that point she needed me there and I wasn’t able to be there because I was in training camp," he said.

All of this played a role in what happened over the next few months -- Harrison's request for a trade, his down season, his contemplation of retirement and ultimately his release from the Lions. He said he intends to play in 2020, calling his retirement comments emotional, and clarified he has no ill will toward Patricia. It was just time for a change.

"Matt Patricia’s a great coach, a great guy," he said. "I have a lot of respect for Matt Patricia. It had nothing to do with him personally."