Clint Dempsey was sent off following a video review and the Seattle Sounders suffered a 3-0 defeat at FC Dallas on Sunday.
Dallas was already leading 1-0 when Dempsey was dismissed in the 37th minute for hitting out at Jacori Hayes as the two battled for position.
Although the referee did not immediately see the incident, replays showed Dempsey lashed out behind him to strike Hayes, and the U.S. international was sent off following a review.
Dempsey will be suspended for at least the Sounders' game against the Montreal Impact on March 31, though MLS could add to that ban because of the violent conduct.
Dempsey also sarcastically applauded the referee as he was shown the card, an action which has led to increased suspensions in European leagues in recent years.
Michael Barrios set up Roland Lamah to tap in FC Dallas' opener in the 20th minute, and the hosts doubled their lead in the 58th minute when Maxi Urruti lashed in a low shot from 20 yards.
Lamah then scored his second of the day to make it 3-0 with a chip in the 63rd minute to heap more misery on the Sounders, who have now lost the first two games to open the season and also crashed out of the CONCACAF Champions League in midweek.
Asked about Dempsey's red card at half-time, Sounders coach Brian Schmetzer told the television crew that with the presence of video review players can't do something "stupid." He then told reporters after the game that Dempsey's red card made an already difficult task even harder.
"Well, it's not good enough, number one. We need to play better," he said. "I don't mind if teams beat us and they play better than us, but before the red card, we didn't play up to our potential.
"That's something I have to take responsibility for, making sure the team comes out right, plays better, and away from home it's always difficult. There are always challenges here in Dallas, and after the red card it was an uphill battle, for sure."
FC Dallas, which fell out of the CCL in the previous round, won its first MLS game of the year after earning a draw in its season opener.