On Sunday following their 31-26 win over the Giants, he was able to breathe a sigh of relief. It wasn't a glittering performance, but the Lions bottled up the run for the first time this season and finally controlled the line of scrimmage with their ballyhooed defensive line.
"It was long overdue. We needed a game like this, and I'm just happy it came against my former team," Harrison said with a smile.
Snacks instantly transformed the Lions defense upon his arrival last season. They smothered the run down the stretch, fueling expectations for this season. Then they allowed over 100 yards on the ground in each of their first six games. They entered Sunday second to last in the NFL in total defense.
And here came Saquon Barkley.
"We had a conversation among ourselves and just said it was time to make a change. Guys needed to be more aggressive, myself included, and we just needed to cut down on the mental mistakes," said Harrison. "I think for the most part we did that."
Harrison, who briefly left the game with a hamstring injury, finished with three tackles, all of them against Barkley. He said afterward he felt "fine." Tied for the team lead with seven tackles was linebacker Devon Kennard, who also scooped up a Daniel Jones fumble and returned it for a touchdown in the first quarter.
Like Harrison, Kennard was frustrated last week with the defense. "Ridiculous," he said of their inability to stop Dalvin Cook. He was in a much better mood a week later.
"For us to be able to stop the run -- I think they ran for less than 100 -- that's one of the first things I always look at when I get in the locker room," said Kennard. "I feel like we did a better job stopping the run against a very talented back, one of the best backs I've ever played against personally."
The Lions also finally mounted a pass rush on Sunday. It's been a struggle this season, but they sacked Daniel Jones three times and hurried him a handful of others. Two of those sacks belonged to Trey Flowers, who tripled his season total in one game. That's what the Lions expected out of Flowers when they inked him to a $90 million contract in March.
And it's what Flowers expects out of himself.
"It definitely feels good," he said. "A lot goes into a sack. The preparation, the hard work individually and then obviously collectively, guys making him hold the ball and keeping him in the pocket. To get home and to create a big play feels good."
The pass rush was limited prior to Sunday in part because the Lions weren't bringing much pressure. Matt Patricia appeared to dial up more blitzes against the Giants, especially with his linebackers.
In reality, said Patricia, "It was just probably a little bit more pronounced. I think some of those calls have been made previously and maybe not noticed from that aspect of it. Just glad that we executed, to be honest with you."
Perhaps most importantly, the Lions stiffened down the stretch. They've coughed up numerous late leads this season, and entered Sunday with the second worst fourth quarter scoring defense in the NFL. They did surrender another late touchdown, but this one didn't cost them, thanks to a pair of fourth down stops that came before it.
"I feel like we've played really good ball at times, but some of the losses we've had we didn't finish, even the tie early in the year," said Kennard. "To be able to get some stops late in the game, that's something I'm really proud of. We stopped them when we needed to stop them and put ourselves in a position to win."
It was a game the defense needed badly, and a win the Lions needed worse. It wasn't perfect and the Giants aren't exactly a measuring stick, but Detroit is through the toughest stretch of its schedule. They get the Raiders next, then the scuffling Bears, two opportunities for the defense to build on what it did Sunday.
The onus to improve remains, but at least some of the frustration is gone.
"It's not really a wait off our shoulders, because we have to do it again next week," said Harrison. "We have to be consistent, it can't just be one game. But it's a step in the right direction."