Grosjean and Rossi made contact, knocking them both off course, and resulting in an argument over the team radio.
Team owner Michael Andretti was then seen in a heated debate with Rossi’s father.
Grosjean fumed on the team radio about Rossi: “What the hell is wrong with him?”
Grosjean was then asked by his team to hold up traffic to help Rossi – but he refused.
“Because Rossi put me in the wall, so I am not going to protect him,” he argued.
Grosjean also made contact with fellow Andretti driver Colton Herta. Rossi bumped teammate Devlin DeFrancesco.
Herta finished IndyCar at Mid-Ohio in 15th, DeFrancesco was 17th, Rossi was 19th and Grosjean was 21st.
Grosjean said afterwards: “I must apologise to Colton.
“I had a lot more grip than everyone else so I just braked. I didn’t realise Colton would brake so early. So I tried to avoid contact.
“That wasn’t good from my side, but I think that’s going to be it as far as today, it’s just that Rossi is an absolute idiot out there.
“I don’t know why he does that.
“He’s on black (tires), I’m on reds. I’m on the outside, and I carry more speed through the corner. He did it once on the restart. OK, maybe he slipped on cold tires.
“Do it again the next lap, then he did it on purpose. My hand is hurting. We lost the bloody race.”
Rossi said: “Just a racing incident.
“He was on a softer tire and probably going to get around me, but he likes to do it fast and early. I had to test him there and obviously that’s unfortunate to tap into a teammate, but that’s the way it goes.”
An Andretti statement said: “A round of incidents amongst teammates cost valuable track positions. The melee brought about high tensions and lowered finishing results.”
Michael Andretti called a furious team meeting afterwards.
“It wasn’t pleasant, but it was good that he did it,” Grosjean said. “I understand he’s frustrated and not happy with us.”
Grosjean and Rossi are F1 veterans while Michael Andretti is linked with entering a team into F1.