The build-up to the weekend has been dominated by the "consequences" imposed by McLaren on Norris after the team held him responsible for banging wheels with Piastri in Singapore a fortnight ago.
That minor tap paled beside the carnage at turn one of Saturday's sprint in Austin, Texas, as Norris was left with only three tyres on his car.
Starting from third, Piastri – who leads Norris by 22 points in the championship standings – attempted to cut back up the inside of his teammate but turned into Sauber's Nico Hulkenberg and, as a result, smashed into the rear left of Norris's car.
Norris was spun round as his left-rear tyre was sent careering across the track. Piastri limped on briefly but suspension damage also put pay to his involvement in the 19-lap dash, in which Max Verstappen clinched victory.
McLaren's decision to involve themselves in the title fight by sanctioning Norris after Singapore will prompt questions over what they decide to do after this latest collision.
However, McLaren CEO Zak Brown told Sky Sports from the pit wall: "That was terrible. Neither of our drivers to blame there.
"That's some amateur-hour driving by some drivers up there at the front, (they) whacked out two guys.
"I want to see the replay again but clearly Nico Hulkenberg drove into Oscar and he had no business being where he was, he went into his left-rear tyre."
Piastri said: "It's obviously not ideal, but I actually haven't seen what happened yet," he said.
"I tried to cut back on Lando - I mean, we were both very far from the apex and then got a hit, and he obviously sent me into Lando, so (it's) a shame."
Norris said: "I mean, what was I meant to do in that - I just got hit. I did nothing wrong. Further back things happened, and I just got unlucky and I got hit because of it."
He added: "I need to look a bit more carefully. It's more people further back just being a bit careless, and we are the consequence of that."
McLaren have further cause for concern in the shape of Verstappen. The crash threw the door wide open to the Dutchman to claim victory as he looms ever larger in the championship picture.
His eight points for winning the sprint means he has cut Piastri's advantage to 55 points and trails Norris by just 33.
Starting from pole, Verstappen was clear of the first-lap chaos – where Hulkenberg and Fernando Alonso were also eliminated – and he led away from George Russell at the safety-car restart.
But Russell was intent on making a fight of it as he lunged up the inside of turn 12 on lap 19 but failed to make the corner as both cars were forced off track.
Verstappen pulled clear after that incident to claim a routine win as Carlos Sainz – starting from seventh – took an impressive third for Williams.
Lewis Hamilton finished fourth ahead of Ferrari teammate Charles Leclerc.
