Houston’s Andre Hainault is shown battling United’s Lionard Pajoy during Sunday’s first game of the Eastern Conference finals. (Bob Levey/Getty Images)

A Houston Dynamo defender should have been ejected for taking down a D.C. United player and denying a goal-scoring opportunity in an MLS playoff match last weekend, the head of a referee group said Wednesday.

However, the league’s disciplinary committee decided not to take retroactive action against Dynamo defender Andre Hainault, clearing him to play in the second leg of the Eastern Conference finals Sunday afternoon at RFK Stadium.

Peter Walton, general manager of Professional Referee Organization, which oversees officiating in the United States and Canada, was in attendance last Sunday in Houston and said afterward that referee Ricardo Salazar should have called a foul and issued a yellow card for Hainault’s tackle on Raphael Augusto just outside the penalty area.

He also said, however, a red card was not warranted because another defender could have intervened had the tackle not occurred.

But after reviewing video of the incident, Walton wrote on the group’s Web site: “It is clear it ticks all the boxes for a denial of a goal scoring opportunity and a send-off should have been the outcome.”

He also wrote: “My opinion has changed in as much as the [other] defender, which I thought in real time would have influenced the play, clearly was behind the action.”

United was leading 1-0 when Augusto touched the ball past two defenders and surged toward the net. He and Hainault were shoulder to shoulder, and as Augusto sought control, Hainault yanked him down by the arm and then appeared to scissor-kick the Brazilian midfielder’s legs.

Salazar allowed play to continue.

The next day, in response to questions from a pool reporter, Salazar said: “I judged this play as two guys coming together and no offense was spotted. . . . Based on my angle there was contact by both players and therefore no offense was identified.”

United players and coaches were furious about the decision. Had it been ruled a red card, D.C. would have had the clear upper hand in the second half. Six minutes after halftime, Hainault scored the equalizer. Houston added two more goals against unraveling United to take a commanding lead into the final leg of a series determined by total goals.

Dynamo Coach Dominic Kinnear told the league’s Web site he “wouldn’t have complained one bit” had his player been ejected.

Told of Walton’s post-video comments, United Coach Ben Olsen said in a sarcastic tone: “Oh, he did? Huh?” He then added: “I absolutely agree with him. . . . It was a real call that could have changed the course of this series, and it’s disappointing.”

MLS’s five-member disciplinary committee reviewed the incident but decided not to take action. Under the guidelines, when a referee sees an incident and doesn’t act, the committee will not issue a suspension unless it decides unanimously that both a red card was deserved and “the play in question is of an egregious or reckless nature.”

People familiar with the decision said the committee was unanimous about a red card but not the second part.

For its part, United was more concerned about the status of three injured starters than disciplinary matters. Chris Pontius (groin), Marcelo Saragosa (hamstring and knee) and Brandon McDonald (calf) did not practice and are listed as questionable.

Upon receiving results of MRI exams, Olsen was upbeat about Saragosa and McDonald playing Sunday but remained concerned about Pontius, the team’s top scorer with 12 goals.

“We have to evaluate them day to day,” he said. “We’ll see about Chris. Chris at this point looks a little more severe than the other guys, but there’s still a chance he will be okay as well.”

United notes: MLS fined goalkeeper Bill Hamid and forward Lionard Pajoy undisclosed amounts for behavior after Hamid’s red card last Thursday in the second game of the semifinal series against New York. Hamid didn’t leave the field in a timely fashion and Pajoy scuffed the penalty spot with his cleats.