This is the second season for the Giants defense under Steve Spagnuolo, so when they are installing the system in training camp they go to the obvious source to see how it’s supposed to look: last year’s game footage.

There’s just one problem.

“It’s tough to watch sometimes,” linebacker Jonathan Casillas admitted on Thursday. “Sometimes it doesn’t look quite how we want it to look.”

Probably more than sometimes. The Giants are coming off a season in which their defense ranked near the bottom of the NFL in virtually every significant statistical category and finished 32nd — last — in total defense. Reliving those plays for those who are returning can be painful.

“It’s tough to swallow when you wear that number on your back, No. 32, that’s tough” Casillas said of the ranking of the Giants defense in 2015. “We’re all grown men, responsible and hungry human beings, and we want to do better, and we will do better.”

Of course not everyone has the same bad memories. There are enough new players to keep the keel of the room fairly even while glancing into recent history. Many of them, such as Olivier Vernon and Janoris Jenkins and Damon Harrison, are here directly because of the woeful 2015 season they see flash before their eyes.

advertisement | advertise on newsday

The good news is that there is every reason to believe that the Giants defense this season will be better. They can’t be worse, at least.

Spagnuolo stopped short of admitting what just about everyone thinks, that he has better talent on defense this season.

“If I say that, that would be an injustice to the guys we had last year,” he said. “I’ll let you judge that, but I’m just glad we have the guys we have right now.”

While it’s difficult to go back to last season and think about how awful that defense was at times, Casillas said it continues to hang over the group.

“It’s like the elephant in the room,” he said. “It’s hard not to say every now and again. If we feel like we’re being content in any way, the number will be said by somebody.”

Giants videos

To what degree they improve this season will likely be the factor that determines whether they find success as a team. Last year it did.

“I feel like we let [Tom] Coughlin down,” Casillas said of the coach who was replaced after a second straight 6-10 season. “It was a tough year. Our offense did what they were supposed to do in a lot of games, and defense didn’t pull through when we were supposed to in a lot of games. Some games we played well, some games at the end of the game, we didn’t do what we were supposed to do. That’s us. We got to take it, it’s myself, Spags, all the linebackers, the d-linemen, the new guys coming in. We’ve all got to wear that. And we’re here to rectify that.”

If they’re successful at that, next summer’s installation of the defense will be a more pleasant viewing experience.