Real-life brothers-in-law Jake Gyllenhaal and Peter Sarsgaard are adversaries in 'Presumed Innocent'

Occasionally, while filming an intense courtroom scene for his new series, Jake Gyllenhaal would catch his ''Presumed Innocent'' co-star Peter Sarsgaard glaring at him from across the room.

''It was just funny,'' recalled Gyllenhaal in a recent interview alongside Sarsgaard, doing a quick impression of Sarsgaard's stare.

''It's like, ‘OK, OK,''' joked Gyllenhaal as if to say ''tone it down" as Sarsgaard cackled at the commentary.

The two rib each other like family because they are family. Sarsgaard is married to Gyllenhaal's older sister, actor and director Maggie Gyllenhaal.

It's not Gyllenhaal and Sarsgaard's first time acting together, either. They also co-starred in 2005's ''Jarhead'' and 2007's ''Rendition.'' But ''Presumed Innocent'' is their first series together (and Gyllenhaal's first TV show ever) — and marks the first time they're playing adversaries.

Premiering Wednesday on Apple TV+, ''Presumed Innocent'' is based on the legal thriller novel by Scott Turow that was originally adapted as a 1990 film starring Harrison Ford.

Here, Gyllenhaal plays Chicago prosecutor Rusty Sabich, charged with murdering his colleague — an accusation that has fractured the district attorney's office. Sarsgaard is attorney Tommy Molto, another co-worker intent on proving Sabich's guilt. Meanwhile, Sabich's marriage to Barbara (Ruth Negga) is falling apart under the weight of the accusation and the potential he could be found guilty.

''It's a little bit like a football quarterback coming up to the line at some point and looking at what you've got in front of you ... and seeing where the opportunities lay,'' Kelley said.

O-T Fagbenle, who plays attorney Nico Della Guardia, also enjoyed watching the two spar.

''I'm an ignoramus. I only found out on set that they were related,'' Fagbenle said. ''They got on great, obviously, but they really have brotherly kind of, you know, roughhousing. Not physical but like verbal. And so when I saw them, I was just like, ‘Oh, wow, there is such a history between you two.'''

Gyllenhaal agrees that shared history is what makes them able to push each other's buttons as needed.

''I love him so deeply, which comes with all the complications too,'' Gyllenhaal said. ''We've been through so much together, and so we can bring those things out in the fictional world.''

''Everyone is excited for it,'' Gyllenhaal said. ''Like, ‘What's Peter going to do today?'''

They also have the comfort and trust to give each other notes on what to play up, what to dial back, or perhaps interpret differently.

''Jake will be like, ‘I see what you meant, but I don't think that's actually reading the way you think,''' said Sarsgaard. "That's someone who's really, really listening to you. Even if you have a great director, it doesn't read like someone who really knows you and sees you as an artist. This family has a very special connection that way. We're very good at witnessing each other.''

Filming a series for the first time, says Gyllenhaal, ''was a fascinating process, one I've never had and one you don't have on a film,'' he said. Having new scripts to memorize meant his ''acting muscles and tools were being used constantly.''

''You go from scene to scene to scene and it's kind of nice actually, once you get into the rhythm of it,'' added Sarsgaard. ''I have more trouble with big movies where you have hours in between setups to do a close up, and in a couple more hours we're going to do the wide shot; I've forgotten everything. I have no idea what's going on.''

''I wanted to know but it was being written as it went on,'' said Gyllenhaal, likening it to how the public waits for a trial verdict in real life.

The courtroom scenes gave various actors an opportunity to shine, affording each one a chance at a big speech.

''Everyone had a day where they did it, or a couple of days, where it was your time,'' said Sarsgaard. ''There's something as a performer that comes alive when it's your time and that's a nice feeling. It's kind of a recharge in the middle of filming a lot of other things.''

''It's fun giving each character a moment,'' added Kelley, who attended law school ''in the early '80s.'' He has put the tuition money to good use over the years, writing a number of hit legal-centric shows including ''Ally McBeal,'' ''Boston Legal,'' ''The Practice'' and ''The Lincoln Lawyer.''

He had in fact practiced law until he got a job on ''L.A. Law,'' which debuted in 1986.