(CNN) -- Cleveland police have slammed Cleveland Browns player Andrew Hawkins for wearing a T-shirt calling for justice in the police shooting of 12-year-old Tamir Rice during a warm-up before Sunday's NFL game against the Cincinnati Bengals. Jeffrey Follmer, president of the Cleveland Police Patrolmen's Association, criticized Hawkins' on-field protest. "It's pretty pathetic when athletes think they know the law. They should stick to what they do best on the field," Follmer told CNN in a statement.