Rossi and Grosjean were jockeying over 10th and 11th on lap 58 of the Honda Indy 200 at the Mid-Ohio Sports Car Course when they came to blows out of The Keyhole.
Shod with the softer compound tyres, Grosjean sought to go around the outside of his stable-mate only for Rossi to hang the Frenchman out to dry on the corner exit.
Stan Sport is the only place to watch the 2022 INDYCAR Series with every race streaming ad free, live and on demand. Start your free Stan Sport trial here!
One lap later, the four-time Formula 1 podium finisher tried the same move but made wheel-to-wheel contact.
That speared Grosjean out into the weeds and nose-first into the tyre wall. Rossi, meanwhile, carried on unabated.
“What is wrong with him?” Grosjean screamed over the radio.
The Safety Car duly made its way out onto the course to neutralise the race leaving Grosjean to shake his head in disgust.
READ MORE: Legend calls for ‘respect’ after Kyrgios furore
READ MORE: Formula 1 young gun survives horrific crash
READ MORE: Raiders fume at controversial call that baffled greats
READ MORE: Volkanovski retains title in dominant bloodbath
Rossi radioed to his team that the incident was unintentional. Grosjean, however, did not see it that way and remained incensed for the rest of the race and some time afterwards.
Having dropped a lap to the leaders, the No.28 made little effort to help his stable-mate.
“What do you want me to do, just block everyone behind and not go ahead?” Grosjean asked his team.
“[We] want you to protect your two team-mates up front,” his crew chief replied.
“Because Rossi put me in the wall, so I’m not going to protect him,” the driver fired back.
Post-race, the four-time IndyCar Series podium winner continued his tirade.
“He’s an absolute idiot, sorry,” said the enraged Grosjean.
“I don’t know why he does that. He’s on blacks [hard compound], I’m on reds [soft compound], I’m on the outside, carrying more speed into the corner.
“He did it once on the restart and I thought, ‘okay, maybe he slipped because he was on cold tyres’ [but] did it again the next lap and did it on purpose.
“My hand is hurting. We lost the bloody race.”
The race was one to forget for Andretti Autosport on the whole.
Front-runner Colton Herta dropped out of contention when he failed to pit before a full course caution, which left him high and dry and unable to stop for fuel and tyres under yellow.
Herta’s day only got worse when Grosjean fed him off into the grass late in the race courtesy of a hit from behind.
Meanwhile, Rossi and rookie stable-mate Devlin DeFrancesco banged wheels to add salt to the wounds of the team.
In the end, Grosjean wound up 21st with Rossi just ahead of him in 19th. DeFrancesco was 17th while Herta recovered to 15th.
Grosjean conceded he was at fault for the Herta clash, but couldn’t let go of the Rossi incident.
“One thing I want to say, I must apologise [for] Colton,” he added.
“I got caught because I was catching the pack on really warm tyres and had a lot more grip than everyone else. I just braked and I didn’t realise Colton would brake so early, so I tried to avoid contact.
“It wasn’t good from my side. I think that’s not the biggest part today, it’s just Rossi’s an absolute idiot out there.”
McLaughlin celebrates with a shoey
Rossi, however, downplayed the fracas.
“Yeah, that was just a racing incident,” the American explained.
“He was on the softer tyre and probably was going to get around me. He likes to do it fast and early.
“I had some understeer there and obviously that’s unfortunate to happen to a team-mate, but that’s the way it goes.”
Rossi, who is set to leave Andretti Autosport at the end of the year for McLaren SP, denied suggestions the impending exit played any part.
“No, of course not, we’re team-mates,” he said.
“We’re driving for Andretti Autosport to get the best result possible.”
The incident caught the ire of team boss Michael Andretti, who pulled the two heads together post-race.
“Michael just talked to us, which obviously wasn’t pleasant, but it’s good that he did it,” said Grosjean.
“I understand that he’s frustrated and that he’s not happy with us.”
Team Penske’s Scott McLaughlin won the 80-lap affair, moving him from ninth to seventh in the standings.
The IndyCar Series continues in Canada with the Honda Indy Toronto at Exhibition Place on July 18 (AEST).
For a daily dose of the best of the breaking news and exclusive content from Wide World of Sports, subscribe to our newsletter by clicking here!