DC United forward Eddie Johnson has been fined by the MLS Disciplinary Committee for an incident with FC Dallas player Zach Loyd during a match last month.
The league announced a string of new rules at the start of the season designed to crack down on perceived ill-discipline.
One rule dealt with players raising their hands to their opponents - which Johnson fell foul of during DC United's showdown against Dallas last month.
During the game, the 30-year-old appeared to push Loyd in the face while trying to get on the end of a set piece. The amount Johnson has been fined wasn't disclosed.
Vancouver Whitecaps back-up goalkeeper Paolo Tornaghi has also been reprimanded by the league for breaching another of the new rules - infringing on the field of play.
Tornaghi came on to the pitch in the dying minutes of Vancouver's game against Real Salt Lake - that has earned him an undisclosed fine and a one-match ban.
Last week, both Columbus Crew and Chivas USA were given an official warning after a clash between players from both teams during a recent match, while midfielder Bernardo Añor was fined for sparking the bust-up.
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