Credit: John P. Fleenor/HBO

Game, set, longest bloody match in tennis history. On Saturday at 10 p.m., HBO will air the mockumentary 7 Days in Hell (HBO Go subscribers can watch it early), an absurdist retelling of a fictional weeklong court battle at Wimbledon between an outrageous fallen American star named Aaron Williams (Andy Samberg) and a blockheaded, proper Englishman named Charles Poole (Kit Harington) who is under tremendous pressure to become the first Brit to win the trophy since the 1930s.

EW served up a few questions to Samberg about this ballsy (in more ways than two) project, which he also executive-produced.

ENTERTAINMENT WEEKLY: How did this come about? And were you watching the longest real-life tennis match [a 2010 first-rounder at Wimbledon between John Isner and Nicolas Mahut that lasted 11 hours and five minutes over three days] in real time?

ANDY SAMBERG: The writer of 7 Days of Hell, Murray Miller, is an old friend of mine from summer camp, and when we were that age — probably about 17, 18 — we already were writing comedy stuff together. We both played tennis and wanted to do something with comedy and tennis, and it was sort of a pipe dream. And we were watching the Isner-Mahut match together on the third day and laughing about how long it was going. We were saying, “Man, somebody should write a movie where a match just never ends.” And I said, “We should! We should do that! We both work in the comedy business — why not just do it?” [Laughs] A year and a half ago — he is a writer for Girls and has a relationship with HBO — I said, “Hey, instead of trying to make that a big movie, let’s make it documentary-style and pitch it to HBO.” So we pitched it and they liked it and then we made it. It happened really fast.

How would you describe this mockumentary? Equal parts epic and absurd?

Yeah. Format-wise, it is in the vein of things like Christopher Guest and those guys. But there has been such a rise of the sports doc on television, especially with HBO Sports, 30 for 30, E:60, all that stuff. We were also inspired by McEnroe/Borg: Fire and Ice that HBO made, which we love. There’s parts of that that sort of sneak in, too. It’s for people who love tennis and for people who love sports docs and for people who love crazy comedy — and for people who love HBO comedy because it’s very dirty. It was kind of a fantasy-camp thing for us to shoot a comedy on grass courts. [Laughs]

So, whom is it not for?

I would say it’s maybe not for young children. There’s a graphic nature to it.

How much tennis training did you do for this role?

I did zero active training. I played a little when I was a kid. My mom is a big tennis player. But I had actually played the sport before, which is more than I can say for Kit, who took one lesson the day before we started shooting. [Laughs]

Come on, Kit. Commit to your craft!

We were just happy he showed up, man. We love Kit. But once we got him in the tennis whites, it all kind of came together.

Why him? Besides Game of Thrones, obviously. What made you think that he’d be perfect for this?

When we conceived this thing, we wanted it to be an American bad-boy lunatic against a straight-laced Brit with the weight of the British hopes on his shoulders. We had conceived it before Andy Murray actually won [Wimbledon in 2013], so it was still being written in the midst of that crazy drought. And we play it as such in the piece that Andy Murray hadn’t won yet, because it’s in the past. So, we knew that we wanted somebody who could play Brit really well and then we were talking about who was out there and who was the right look. And I’m a massive Thrones fan and Jon Snow is the greatest. I bumped into Kit at some event and he was super nice, and I was thinking that he could probably play it really well. And we had a meeting and he told me that he actually had done some comedy stuff when he was in college and that he always liked playing kind of “the thick bloke,” as he called it. He read the script and just loved it.

Using tennis terms only, how would you describe Kit’s comedic chops?

An ace right up down the line.

When Andy Murray won Wimbledon, were you like, “Uh-oh. How does this affect our project?”

No, not too much. It was already set in the past because it’s a doc looking back, which is such a valuable format. We could just sort of slide the year to exactly what we needed.

Any anecdotes from filming?

We shot in Palm Springs for the Wimbledon court because they had a grass court. We built up a lot of the structure around the sides. And it was 122 degrees the whole shoot, which was miserable, but it helped Kit and I to look like we’d been playing tennis for seven straight days because we were exhausted within five minutes. So we could pretty much shoot in any order and it would look pretty miserable. It was fun. We stayed at the hotel shot for a few days and got out of there. Certainly I bore my soul to all of those wonderful people who came and sat in the heat and pretended to be watching fake tennis.

How would you tease the streaker scene that’s in the trailer?

There is some beautiful and very human physical interaction on the court. And then some slightly less beautiful but still very human contact. [Laughs] I believe when Wolf of Wall Street came out they said it was a throwback to Caligula and I would say then this is almost a throwback to Wolf of Wall Street.

There are many big guest stars [including Lena Dunham, Will Forte, and Michael Sheen, as well as tennis figures like John McEnroe, Serena Williams, and Chris Everet]. Was it pretty easy to get them on board?

Surprisingly, yes. A lot of the folks we asked were friends and then a lot of folks were just people who responded to the material, which is always the dream. And the thing people kept saying to us when they came in was: It was just so wild that they wanted to do it. It’s so rare that they get stuff sent to them where it’s like really big, hook-y jokes. We decided we wanted to go full-on crazy with this one. And it seemed like there was an appetite for that among the people that we asked, so we felt really lucky.

Did some of the non-actors like Serena Williams and Chris Evert require more explanation or instruction than your comedy friends, who are used to just going with these kinds of things?

They all pretty much got it. Those are all savvy folks. McEnroe, I have worked with a few times before because he was in a few Digital Shorts. And he’s obviously hilarious. Chris Everet, I’ve always been a huge fan of hers but she was really funny and totally got the joke. She even added some stuff that was really great. And Serena, I’d never met before but I’ve been a huge fan of hers forever. I actually saw her win Wimbledon a few years ago because I was in England shooting a show and I went live and it was one of the coolest things ever. We flew to her and shot with her. Some of her line readings are so subtle and she just fully grasped the whole deal and I loved how real she was with it all. The tennis players are representing themselves and selling the reality of this world. The more they played it real, the funnier it was, and I think all three of them did a great job.

Did you try to get Andre Agassi for a cameo? There are all of these Agassi touches to your character.

There are some Agassi touches. I don’t remember at this point, honestly, if we asked. I think maybe we did and it was his schedule or something. Maybe we didn’t. We should have. I mean, when I was a kid, he was fully one of my heroes. I just loved that dude and the style of it. And probably the thing I take away the most joy from the whole experience is [the] wardrobe [department] got me some of the actual Nikes that he wore during that era, and I wear them in my daily life now. Those high tops with the crazy colors are so awesome. But Aaron has some Agassi, he’s got some Borg, he’s got some McEnroe, there’s some Krickstein.

Who were the influences for Charles Poole?

Just every male Brit player that tried to win Wimbledon over the last 40 years. Certainly the original idea for it was loosely Andy Murray, except then when we were trying to think of a comedy angle, it diverted because we wanted him to be dim, and that is clearly not the case with Andy Murray. But the jump-off for it was whoever the most recent person that had the weight for a Brit to win and then we just started spinning it to be like: Who would be the opposite of Aaron Williams, style-wise? In a lot of ways there is the Fire and Ice thing, too — Borg was so quiet and understated. There is Borg in Aaron [too], because Aaron has an underwear line.

What should people brace for when they sit down to watch 7 Days?

Hopefully, a lot of laughing. We’ve had a really good response from people we’ve shown it to. The comment we get back the most is, “Wow — that was way crazier than I was expecting.” In a good way. But we were thinking, “When is the next time we are going to make a fake documentary about tennis for HBO and be able to do any joke we can think of?” So we kind of threw the kitchen sink at it.