The Super Bowl? Of course he'll be watching. Ditto Monday's first-ever college football final.
"I watch as a fan," says the now-retired defensive lineman.
"I watched the LSU game... I watched Alabama-Ohio State which I thought was a great ball game. I watched a little bit of (the lopsided) Oregon-Florida State until I couldn't take it anymore, and had to turn the TV off."
Despite the toll taken by 12 seasons in the National Football League, most of them with the New York Giants, Marshall still loves a good football game.
He's not alone: even in this annus horribilis for the sport off the field, America can't quit football, either.
In a season marked by domestic-violence scandals, coverup accusations, the suicide of a concussion-suffering college player and a potential US$1 billion brain-injury settlement process between the NFL and former players (Marshall is among the plaintiffs), football is smashing ratings records:
— College games twice set records for American cable-TV viewership — both in the same day. A pair of Jan. 1 bowl games each drew more than 28 million viewers, about 40 times the typical audience for Canada's university final, the Vanier Cup. Even more are expected for Monday's inaugural final, featuring Oregon and Ohio State.
— The 2014 Super Bowl had the biggest-ever network audience in U.S. TV history, with more than 111 million viewers. The biggest audience in Canada for a Stanley Cup game was in 2011, when the Vancouver Canucks faced the Boston Bruins: 8.76 million.
It's a full-fledged cultural phenomenon that extends beyond sport itself.
Tailgate parties aren't just full-day affairs that prompt people to carry generators to stadium parking lots so that they can power their sound systems and TV screens. They've even evolved into a cuisine genre, as immortalized in the Food Network's "Tailgate Warriors" show.
The pulsing heart of America's love affair beats mightily in Texas high schools, as famously documented by the book, film, and TV series about Texas high schools in "Friday Night Lights."
There were more than 52,000 people at one of the Lonestar State's high-school championship games this year — still short of last year's record 54,347.
The passion is also palpable in big eastern cities, including the toniest tracts of the U.S. capital.
One night last spring, in the midst of the hockey and basketball playoffs, the noisiest crowds at a sports bar near Capitol Hill huddled around screens showing the NFL draft; fans of other sports discreetly took in their own playoff games in quieter corners of the bar.
Try striking up a conversation about most sports and you'll get a polite response at a barber shop on 18th Street. But bring up football, and the shop springs to life with the sound of barbers bantering with cape-clad customers.
Many still remember Marshall for the sternum-bruising smash that helped end Joe Montana's legendary stint with the San Francisco 49ers.
These days, however, Marshall wants the game to change.
"I was told as a kid, 'Hit what you see and see what you hit.... Plant that (helmet) in the centre of his chest. And if you rupture his spleen or you rupture his chest as a result, oh well, that's part of the game,'" said the two-time Super Bowl champ.
"'And if you see the brown spots and things seem to start moving a lot slower for you, just rub a little dirt on it and get back in there.'"
He's spoken with many retired players about the cognitive and emotional problems they've been having: "It's your ability to recall. It's your ability to make good decisions. It controls your emotions — or lack of emotions. Your mood swings. Your inability to sleep... Depression. Anger. A short fuse. You hate feeling like this."
One of the people he talked to was a former teammate, Dave Duerson. Duerson later took his own life by shooting himself in the chest and leaving a suicide note requesting that his brain be sent to a lab for analysis.
Duerson was diagnosed with chronic traumatic encephalopathy, or CTE. Marshall has since been diagnosed, too. Suicidal thoughts are a rampant problem for former players suffering from CTE, he says.
Marshall now works with a new organization, Brain Unity Trust — co-founded with Pittsburgh lawyer Jason Luckasevich after the pair met through their landmark class-action suit against the NFL, now being settled out of court. He hopes to educate young players, coaches, and researchers about new approaches to tackling and head injuries.
Luckasevich describes how he had to keep repeating himself in a recent conversation with a forgetful ex-player. He tells the story of two others who got into trouble because they forgot they were carrying guns — one on the grounds of a school.
And he marvels at their devotion to the sport that has dealt them such damage.
"These guys get so hostile and talk about how their team let them down, and their union let them down, and the NFL let them down," he said. "And the next thing you know, they're like, 'Oh, I've got a Hall of Fame meeting I've got to go to.'
Despite the fervour, there are signs that football's problems in the U.S. are beginning to take a toll.
Attendance has dipped in recent years — not only in the pros, but at the college level too. Youth entitlement has also seen a decline these last few years, with fewer kids playing in Pop Warner leagues.
The question of whether to register a kid for football is the theme of "The United States of Football," a documentary directed by Sean Pamphilon, a big fan who also happens to be a dad.
In the end, Pamphilon's son opted instead for baseball and guitar lessons. But his father still can't shake the habit.
"I feel like a complete hypocrite when it comes to this," Pamphilon said in an interview with SB Nation following the film's 2013 release.
"Because I've been exposed to an incredible amount of human suffering... But then I went to Seahawks training camp. And I saw Russell Wilson and it was, like, pretty much love at first pass."