Andretti was ahead of Sato and fighting to stay on the lead lap early in Houston on Saturday. IndyCar officials showed him the blue flag -- the signal to move over and let Sato pass. Andretti did not heed the flag because he wanted to stay on the lead lap, and that drew a black flag, drive-thru penalty.
As punishment for ignoring the initial blue flag, IndyCar fined him and placed him on probation for three races, including Sunday's second event of the Grand Prix of Houston. Andretti Autosport was also fined $2,500.
"The blue flag was because (Andretti) was in front of the leader, who had a 4-second lead on his teammate. And we felt he was obstructing the leader by not letting the leader go," said Derrick Walker, IndyCar president of competition.
Sato was leading Saturday's race and Andretti driver James Hinchcliffe was second. Marco Andretti found himself in the mix because an earlier spin had sent him to pit road, and when he rejoined the action, he was ahead of the pack. Being passed by Sato would have put him a lap down.
Walker alleged Hinchcliffe was able to close the gap on Sato from four seconds to about half a second while Andretti was ahead of Sato. And because of rain earlier in the race, track conditions provided "limited places for the leader to get by Andretti," Walker said.
But, Walker noted, once IndyCar had given Andretti the blue flag, Andretti suddenly "went quicker and quicker."
"The leader couldn't go quicker, that's fact that that's what happened," Walker said. "Once he (Andretti) got his car going and up to speed, he'd already been given the blue flag instructions. If he'd moved out of the way right away, it would have been no foul.
"But he continued to fight it, by their admission, that they would keep going because they were in the right. When you get a command from race control, you have to obey it."
Andretti has denied he was intentionally holding up Sato, and said he was simply fighting to remain competitive in the race. He ultimately finished eighth.
"My question was, what would have happened if James was leading?" he said. "It's the 20th lap of the race and the facts are I finished ahead of Sato. Because you have to fight. It's early in the race. If it's late in the race, I would have moved over, they wouldn't have had to tell me to move over."
He insisted he was one of the top-three fastest cars on the track at the time he was told to move out of Sato's way.
His father, team owner Michael Andretti, was incensed at the accusation Marco was deliberately holding up Sato to aid Hinchcliffe.
"That's an absolute lie," he said. "He was faster than Sato, and if Hinch was closing in on Sato, maybe, just maybe it's because Hinch was faster."
A.J. Foyt, owner of Sato's car, alleged the Andretti drivers were following team orders.
"The deal with Marco, I would have to say blocking for his own damn car is a bunch of crap," Foyt said.
Walker, meanwhile, admitted IndyCar has to consider going forward whether Andretti should have been given the blue flag considering his position in the race.
"We need to sit down, and we will internally, and ask if that philosophy is correct," Walker said. "Does Marco deserve the right to fight until the bitter end to stay on the lead lap? We've got a philosophical discussion ahead and we need to put that detail in the rule book, because it's not all there right now."
Drivers apparently questioned it, as well, in Sunday's pre-race meeting, and at least one was in public support of Andretti.
"I completely disagree with the call," Tony Kanaan said. "He was on the same pace and the guy was fighting not to go a lap down and should have the right to fight. He shouldn't be made to move over and give up."