Looking for a name of a short story (pretty old)
"Warrior Race" by Robert Sheckley; here is the Project Gutenberg etext.
about a ship that crashed on a planet
It didn't crash, they made an emergency landing because they were out of fuel:
They never did discover whose fault it was. Fannia pointed out that if Donnaught had had the brains of an ox, as well as the build, he would have remembered to check the tanks. Donnaught, although twice as big as him, wasn't quite as fast with an insult. He intimated, after a little thought, that Fannia's nose might have obstructed his reading of the fuel gauge.
This still left them twenty light-years from Thetis, with a cupful of transformer fuel in the emergency tank.
"All right," Fannia said presently. "What's done is done. We can squeeze about three light-years out of the fuel before we're back on atomics. Hand me The Galactic Pilot—-unless you forgot that, too."
where the natives fought their conflicts by committing suicide to show their bravery (and hoping the enemy was shamed/frightened into surrender).
Fannia was frozen for a moment, unable to believe his eyes. Donnaught halted behind him.
Natives were rushing forward by the hundreds now, their knives poised, screaming at the Earthmen. As they came within range, each native stabbed himself, tumbling on a quickly growing pile of bodies. In minutes the Earthmen were surrounded by a heap of bleeding Cascellan flesh, which was steadily growing higher.
"All right!" Fannia shouted. "Stop it." He yanked Donnaught back with him, to profane ground. "Truce!" he yelled in Cascellan.
The story was pretty old, definitely before 1970s.
First published in the November 1952 Galaxy Science Fiction (with Isaac Asimov's name misspelled on the cover), available at the Internet Archive.
Don't remember many details except it had concluded with the crew of the crashed ship reverse-engineering the thing and threatening to kill the natives BEFORE they could kill themselves and thus depriving them of honorable death.
"I have powerful magic in my ship. I can kill every last man, and then you won't be able to die a warrior's death. Or get to heaven!"
The chief tried to free himself with a mighty surge that almost tore one of his arms free, but Fannia held on, pinning both arms behind his back.
"Very well," the chief said, tears springing into his eyes. "A warrior must die by his own hand. You have won, alien."