The National Basketball Association fined New York Knicks guard J.R. Smith $50,000 for unsportsmanlike conduct after twice tinkering with opponents' shoelaces, the league said on Wednesday.

Smith, who won the NBA's Sixth Man of the Year award last season for his play off the bench, was fined after he attempted to untie the shoelace of the Detroit Pistons' Greg Malone at the free throw line on Tuesday.

He had been warned by league officials to refrain from similar conduct after he untied the shoelace of Dallas Mavericks' forward Shawn Marion during a free throw attempt in New York's 92-80 road win on Saturday.

Smith has a history of rules infractions, including a doping violation during the offseason that landed him a five-game ban to start the current campaign.

He was also fined $25,000 in November for a "hostile" tweet directed at an opponent who questioned the NBA credentials of J.R.'s younger brother, Chris Smith, who has since been waived by the Knicks.