Young -- who caught only one pass in six tries during Sunday's Detroit loss to Green Bay -- openly sulked on the field when quarterback Matthew Stafford didn't throw to him and has complained of his role on the team, The Detroit News reported.
The mercurial receiver was placed on the inactive list for the Lions' Thanksgiving Day contest against the Houston Texans after managing only seven catches for 79 yards over the last three games.
"When you play a game like football, it's a team sport and players have obligations to the team," Schwartz said. "Titus hasn't done a good job of fulfilling those obligations this week and recently."
While Schwartz didn't suspend Young, the coach said he will have to earn his way back into the starting lineup.
"His behavior on Sunday was unacceptable and it hurt the team, particularly on offense," he told the News.