Bo beat me to Dog Day Afternoon.
How about ‘Dirty Mary and Crazy Larry’? The ending is rather abrupt and pretty much perfect.
I’m not sure I’d include this in a list of “naturalistic gritty” 1970s movies – it looks far too slick to me, and too contrived.
To me, it stands out as a movie you don’t have to see if you’ve seen the trailer. I swear, they include all the narrative points in the trailer, and even the climactic stunt. Once you’ve seen the trailer, why shell out to see the actual movie?
I think “Serpico” qualifies.
Jerry Schatzberg’s The Panic in Needle Park, which introduced Al Pacino.
Arguably, William Friedkin’s Cruising, also with Al Pacino.
I’m going to put “Badlands” and “Conrack” out there.
Props to KarlGauss for mentioning “Mean Streets”.
Holy shit dude…I was pondering mentioning ‘Chatos Land’, of which I watched the first ten minutes the other day.
Pa Walton, Simon Oakland, James Whitmore, Jack Palance…all talking over each other in deep unintelligable accents. I loved what I saw.
And yes, despite the inclusion of The Carpenters and Nadia’s Theme…Bless the Beasts and the Children is NOT feel-good.
Great movies mentioned… I’m definitely adding the couple I haven’t seen.
If you don’t like the 70s and want something made fairly recently, check out “Buffalo '66” - i because it’s so great, very realistic, gritty, with very natural acting, and a damn good cast.
I think “Two Lane Blacktop” would qualify.
https://en.wikipedia.org/wiki/Two-Lane_Blacktop
Check out Joe, starring Peter Boyle (and introducing Susan Sarandon). Amazing.
Because it’s a really good movie with a great story and fantastic performances that fit the criteria of the OP. I thought I made clear that I thought that was why someone should watch it in my post; I’m sorry for your confusion.
No confusion. Jaunty criticism isn’t a language everyone is familiar with.
It’s still the only trailer I’ve seen that gives away the whole movie
Deliverance?
The Deer Hunter?
I don’t know. I’ll say right now that I haven’t seen the movie and don’t know anything about it beyond what’s in the trailer. But I don’t feel that trailer gave the entire movie away.
Okay, they gave away the premise; two cops decide to rob a bank. But that’s very common in trailers. You need to tell people the premise to get them to go see the movie.
And the trailer shows that they run into complications during the robbery. I don’t think that’s going to be a surprise for anyone who’s ever seen a movie.
But the trailer doesn’t reveal the outcome of the story. Do the protagonists succeed in their robbery and get away with the money? Or do they fail and get captured? Or somewhere in between?
Even Dwarves Started Small (1970)
Gimme Shelter (1970)
Get Carter (1971)
Godzilla vs. the Smog Monster (1971)
Andy Warhol’s Bad (1977)
Bandits vs. Samurai Squad (1978)
36th Chamber of Shaolin (1978)
Hunter in the Dark (1979)
The Tin Drum (1979)
Hmm.
So you saw them feeding the bearer bonds into the shredder, followed by scenes of a ticker tape parade, and that didn’t suggest anything to you?
It suggests to me that maybe you didn’t link to the trailer you intended to.
One movie that hasn’t been mentioned here that might fit the bill is the original Rocky. Watching that these days, it’s astonishing how jarringly different a film it is from the rest of the series (particularly from Rocky III onwards).
Kelly’s Heroes might not quit fit the gritty/natural requirement (it’s a goofball comedy) but there is realism in many aspects of the way WWII is presented. It’s one of my all time favorite movies.
I am extremely curious to hear the definition of “natural” and “realistic” 
Badlands? Terrence Malick’s Badlands?
I love that movie. I think it’s one of the best movies ever made. And I think Linda Manz’s performance (and especially her narration) is one of the best performances ever recorded on film.
But realistic? No.
Gritty, maybe, I guess. Naturalistic? Not so sure.
But brilliant? Yes. Very much yes.