Mike Webb stated that he gave Rossi a 0.3 penalty to give back the time he gained on Marquez after cutting the S-curves. He understood Rossi was forced off track so the penalty wasn't meant to even anything with Zarco.
MotoGP Race Director Mike Webb has explained why Valentino Rossi was given a 0.3s penalty at Sunday's Austin race.
Rossi straight-lined one of the S-curves after an attempted pass by Johann Zarco resulted in contact between the pair.
The Italian re-joined the track still in third, but with a bigger advantage over Zarco and closer to Marc Marquez ahead of him.
MotoGP Race Director Mike Webb said: "The thinking behind the penalty was that you can't gain an advantage by leaving the track.
There was clearly an advantage because he got closer to Marquez. So we negated that advantage.
"But on the other side, [Rossi] left the track involuntarily. Meaning he was forced off by another rider. If somebody did that deliberately and gained an advantage, the penalty would normally be more than the time they gained.
"In this case, it was clearly not his fault for going off track. But he also has an obligation to not gain an advantage out of that circumstance.
"Because it was clear to everyone, including Rossi, that he had gained on Marc the correct behavior is to realise that he has gained an advantage and give it back. Close the throttle and go back to the position he was before the turn, which was just in front of Zarco and nothing would have happened."
The penalty, to be applied at the end of the race, would only have changed the results if Rossi was less than 0.3s ahead of another competitor.
Ultimately, Rossi claimed second place by a margin of over two-seconds from Dani Pedrosa.
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MotoGP News - MotoGP Americas: Race Director explains Rossi penalty