The USC kicker, typically automatic from 45 yards and in, missed two of his three field-goal attempts in the Trojans' win last Thursday and had another miss erased because of a penalty.
"I don't come out there and miss two field goals," he said Wednesday. "That's just not me. I don't like going out there and missing, and it got to my head."
Asked for reasons why he was so off, Heidari said he failed to properly establish his plant foot on the first miss from 40 yards, midway through the third quarter. The now-permanent switching of holders from Matt Barkley to Cody Kessler had nothing to do with it, he said.
USC coach Lane Kiffin said he heard Heidari was yelling at some Utah fans at one point, "getting into it with them." Earlier, Kiffin said he attributed the misses to Heidari being over-hyped.
Heidari said it wasn't the fans' "fault" he missed -- "I missed those two field goals" -- but he did allow that they played a role.
"The crowd said some stuff," he said. "I just got distracted. I don't know what to say -- I wasn't in the right mindset for the game."
It was his first road game of the season, since, as he said Wednesday, he missed the Syracuse and Stanford trips after tearing the meniscus in his right knee in the season opener.
Heidari now has four total field goal misses in his career, including just two last season -- one of which came while kicking with an injured ankle against Notre Dame.
He said Wednesday he still hopes to feel better in the coming weeks after this injury, which he said occurred on a first-quarter kickoff. He'll resume kickoff responsibilities this week against Washington for the first time since the opener.
Kiffin said he was pleased by Heidari's reaction after Thursday's game. When the coach called him in for a Friday meeting upon the team's return to L.A., Heidari didn't attempt to defend his actions.
"He knew he was wrong," Kiffin said. "And it won't be an issue again."