Warriors coach Steve Kerr discusses the grind that is the 82-game NBA regular season and how the fatigue caused mistakes against the Celtics. (0:31)

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To most of the crowd at The Second City comedy club in Chicago, Steve Kerr is still the Bulls hero who hit that dagger in Game 6 of the 1997 NBA Finals. The titles he later won in San Antonio? A postscript for this audience. The championship he led the Warriors to last year as a rookie head coach? Nothing compared with the punch he took from Michael Jordan!

Actor Jamison Webb is working at The Second City when Kerr and his coaching staff come for the show on a late-January night. During intermission, he sends a runner out to ask whether Kerr might like to step up onstage and do an improv game. "He came out, and the place just erupted," Webb says. "He had everything you need for it, which is just confidence and going with the flow, having a good time and not worrying about how he was looking.

"When you're performing and existing in that state, it really frees you up. You just kind of go into this zone where you're so focused on what's going on in the moment, all the other stuff kind of fades away."

Kerr and his wife, Margot, have been coming to the club since Kerr played for the Bulls in the mid-1990s. They had young kids, and any night out was something to savor. But mostly, they just liked to laugh. He made prank calls to radio shows as a teenager. Legend has it that his mother, Ann, still has a tape of his "greatest hits" somewhere. Now, on an off-night before a game with the Bulls, he's riffing with one of the most famous comedy groups in America.

Kerr gets a huge ovation, and the Warriors' coaching staff laughs hardest of all. It has been awhile since they've seen him cut loose.

Kerr had back surgery in July, just weeks after Golden State won the 2014-15 NBA championship. The surgery created a fluid leak in his spine, which needed to be repaired by a second surgery in September. In late September, Kerr and Margot had a joint 50th birthday party (their birthdays are a day apart). "He put on a really good face," Margot says. "But you could see he was in a ton of pain."

For months, he was a shell of himself, battling intense pressure headaches and searing pain behind his eyes. The worst of it was not understanding what was wrong or knowing whether it would ever get better. As an athlete, you break a bone and the doctor tells you it will heal in four to six weeks. This was different. Kerr had no answers. It wasn't his back that hurt, it was his head. He felt sick, weak, tired and dizzy. He sat out the first 43 games of the season, leaving 35-year-old assistant coach Luke Walton in charge of the best team in the league.

"Of course I get angry and pissed off sometimes," Kerr says. "But I can't hang on that. It does you no good."

He feared he might never feel 100 percent again, but on a January road trip through Detroit, Cleveland and Chicago, he at least wanted to feel more like himself. And so it is that he owns the moment at The Second City. "That was right when I started to feel like I could start to live my life again," Kerr says. "I am coming out of this."

It'd be great to put a bow on this and say that Kerr got up on that stage, crushed it and went back to coaching without any more pain. But that's not how this goes.

There is no satisfactory explanation for why Kerr developed his headaches. A current theory is that the change in the volume of spinal fluid after the initial surgery knocked his body out of homeostasis and contributed to a condition known as new daily persistent headache syndrome. But it's just a theory. He has had a terrible migraine basically every day since July. Some days he'll feel better and go for a hike. Other days he'll be seeing spots and looking for a chair to grab or a wall to lean on so he doesn't fall over.

A few weeks after the Second City night in Chicago, Kerr finds himself in the coaches' office before a game in Phoenix with an ice pack on his neck. It is the last game before the All-Star break, and all he wants to do is get home to San Diego to rest, do some yoga, enjoy the sun, order takeout and binge-watch Netflix. But when he gets home, the family's beloved 10-year-old golden retriever, Oscar, who had been ill, goes downhill quickly.

During the worst parts of the summer and fall, taking Oscar for walks had been one of the few bright spots for Kerr. "It was almost like he waited for Steve to get home so he could say goodbye," Margot says. "It was really sad."

Is it all some sort of test? The universe's way of evening things out for a guy who won five NBA titles as a player and one as a coach? Karmic retribution for being given the opportunity to coach one of the greatest basketball teams of all time? Is there some lesson he needed to learn from all this? Some way his team needed to grow?

"We talked about this, especially when we were really in the midst of it and we just didn't know what was going to happen," Margot says. "Like, what is the lesson? We would sit there and look at each other and just say, 'There's got to be something good that comes out of this. There has to be, because it's the balance of the universe.

"But who knows? We may never know."

Pity feels selfish. What makes him feel better is closing his eyes and remembering the joy of hugging Margot and his three kids on the court after the Warriors beat the Cavaliers to close out the franchise's first title in 40 years.

"I get chills just thinking about it," Kerr says. "As a coach, it takes on even more meaning because you feel responsible for a lot of people and for their happiness and well-being."

His back had been bothering him throughout the playoffs, but he chalked it up to long hours and stress. In Game 5 of the Finals, he made a move that really tweaked it. He might have made things worse by playing beach volleyball and golf the week after the championship parade. Soon, while others were dreaming of how many more championships the Warriors' talented young core might win, Kerr was struggling to walk from his hotel room to the car during the Las Vegas Summer League. Doctors told him he had a ruptured disk.

"He'd walk through the casino and have to stop every 20 yards to sit down at those little chairs they have in front of slot machines," Margot says. "He had no choice, he had to get the back surgery."

On top of the world one night, reeling and writhing with constant pain just a few weeks later. Nothing gold can stay. "It reminds you of how fragile everything is," Kerr says. "It sounds like a cliché, but it really is true. "We're all vulnerable. So vulnerable."

Kerr took care of himself long before the back issues and headaches began. He worked out almost every day. He kept things balanced. When the Warriors had an off-day, he told his staff not to come into the office, and he discouraged his players from excessive media or sponsor obligations. "He does everything right. He takes care of himself, he treats people the right way," Walton says. "Karma should be on his side."

Last season Kerr would come home from road trips and gush to Margot about how much fun he was having coaching this team. "He was just giddy. He was on cloud nine," Margot says. "Because he knew how special this team was and how rare it was to get this kind of group together."

Even this year, as he has endured the worst of it, ask Kerr what he has learned and he'll say how grateful he is. "To do this for a living, enjoy the camaraderie and the lifestyle and how that affects our families, we're some of the luckiest people on earth, we really are," he says one rainy afternoon in Sacramento in early January.

The day before, he'd felt so awful he had to cancel lunch with a friend and postpone this interview.

There are some things a man needs to keep inside.

On Jan. 18, 1984, during Kerr's freshman year at the University of Arizona, his father was shot and killed by political extremists in Lebanon. Dr. Malcolm Kerr was a prominent Middle Eastern scholar and president of the American University of Beirut.

Kerr doesn't like to discuss that time in his life very often. He'll answer a question or two, then politely ask to change the subject. But as he went through hell this summer and fall, he drew on the lessons he learned and strength he found after his father's murder. "Same way," Kerr says. "Just go day by day. Immerse yourself in the things you love and the people you love, and keep moving."

Alone at home and trying to heal himself, he cut out sugar and beer and processed foods. He did yoga and moving meditation. At night, he read spiritual books like You Are Here, by the Buddhist monk Thich Nhat Hanh. He practiced breathing through the unyielding pain.

Margot scoured the Internet looking for novel treatments that might help. She joined support groups of people who deal with chronic headaches. "We didn't do anything for months and months," she says. "Every so often, he would be feeling OK and then the kids would come up with something and we'd decide to go out to dinner. Then it wasn't even worth it because we could tell he was so uncomfortable."

Eventually, the isolation became almost as painful as the headaches. On days that he felt well enough to leave the house, Kerr would watch home games from the Warriors' locker room at Oracle Arena. He'd wait for Walton to come into the coaches' office after the game and say, "Thanks for the win, Luke."

The Warriors went 39-4 under Walton, including a 24-0 start to the season. NBA rules held that all of Walton's wins went on Kerr's permanent record, which meant Walton was coach of the month in November with an 0-0 record.

"It was about our staff stepping up to try to fill the role for a good friend, somebody that we all care about, somebody that obviously put this thing together," Walton says. "It's just us trying to help our players out until our guy gets back."

Assistant coach Bruce Fraser, Kerr's best friend on the staff, made him a deal: He'd stop asking him how he was feeling if Kerr would promise to tell him once he started feeling better.

In December, Fraser sensed Kerr was itching to return to the court. But his friend hadn't said he was feeling better, so Fraser tried to take some of the pressure off during one of Kerr's first road trips back with the team. "On the plane, we were talking about something he wasn't interested in. And he turns to us like, 'Really, that's what you guys are talking about?'" Fraser says. "I'm like, 'See, you really aren't missing much. Just remember this when you're sitting on the couch feeling like you're missing out.'"

It meant a lot to Kerr that the culture he'd built in 2015 was strong and self-sustaining. It validated his choice to promote Walton, young assistant Jarron Collins and advance scout Chris DeMarco up a chair after associate head coach Alvin Gentry left to coach the Pelicans.

"All the guys I hire for the staff are cut from the same cloth," Kerr says. "They're all unselfish and committed to the team but ambitious and hardworking. I think ambition can go two ways. You can be ambitious and be part of the team, or you can be ambitious for your own career. I like people who are ambitious for the team."

Still, he missed being around his guys. The camaraderie, the brotherhood, the inside jokes and silly stories that happen when a group goes through a season together.

In early January, Kerr took the staff out to Caffe Mingo, one of his favorite restaurants in Portland. They all piled into an Uber car together.

"The driver started saying it was bullcrap that I wasn't getting the wins," Walton recalls. "He didn't know Steve was in the back, or he didn't recognize Steve yet. So Steve was like, 'Yeah, that head coach of theirs is a real a--hole. He's only thinking about himself.' Then we all started jumping in. I said, 'Yeah, I think Steve even called the NBA to make sure he got those wins.' The Uber driver was like, 'God, he sounds like a jerk.'"

When they got to the restaurant, special assistant Nick U'Ren thanked him for the ride and said, "Oh, lemme introduce you to our head coach, Steve Kerr."

It was classic. Like old times.

A few weeks later, Kerr stepped onto the stage at The Second City.

Immerse yourself in the things you love and the people you love, and keep moving.

Kerr still hadn't told Fraser he was feeling better. He didn't pack any suits on the road trip through the Midwest. But after the Warriors come home, he starts dropping hints he might return. He jokes with Fraser that he might just decide to coach one night. Fraser smiles and says, "Oh really?"

On Jan. 22, the Warriors begin a three-game homestand, including one against their top rivals, the Spurs, whom Kerr sometimes refers to as the White Walkers from Game of Thrones. When the moment arrives, Kerr keeps it small. Before a film session at the team's morning shootaround before Friday's game with Indiana, he just slips it in: "I'm going to coach tonight."

The players go crazy. If they'd had advance notice, they'd have planned a celebration. Instead, they have to improvise.

During training camp, the Warriors had invited NBA impersonator Brandon Armstrong to make fun of them in ways that would be funny in the moment and on tape for the rest of the season. Armstrong nailed his impressions of Steph Curry and Draymond Green. But he really nailed Kerr.

He'd found video of Kerr celebrating the Bulls' 1996-97 NBA title. Kerr throws his hands up to the heavens and lets out a high-pitched birdcall. Comedy gold. Armstrong mimicked it perfectly, and the Golden State coaches had been showing it in film sessions whenever the team needed a laugh.

When Kerr tells the team he is going to coach again, it is the first thing that pops into Curry's mind. The reigning MVP throws his hands up to the heavens and screeches like a rooster. Steve Kerr wasn't 100 percent yet, but he was back.

"People ask what I learned from being away from the game so long," he says. "Honestly, just that I really missed it."