In October 2003, former world chess champion Ruslan Ponomariov appeared in a Ukraine-Sweden match at the European Team Championships in Plovdiv, Bulgaria. Ponomariov, celebrating his birthday, was presented with gifts by tournament organisers at the start of his game. Shortly thereafter, however, Toncho Demirev disqualified Ponomariov, quoting article 13.4 of the Laws of Chess, making him the first player ever disqualified at a major event. The problem? His cell phone had rung during the match.
[Cell phones are banned to prevent players from receiving advice or accessing computer databases of chess moves online. Ponomariov protested and refused to sign the scoresheets. The overall match ended in a 2-2 draw.]