Evidently clenching your fists and "dehumanizing" stares can get you tackled by police:

New cell phone footage shows Miami-Dade Police officers aggressively pinning an unarmed teen to the ground while choking him. His alleged crime: giving the officers “dehumanizing stares” and “clenching his fists.”

Fourteen-year-old Tremaine McMillan says he was feeding his puppy and playing on the beach with some friends when cops riding ATVs approached him and asked what he was doing. The "peacekeeping" officers say they saw McMillan roughhousing with another teenager, told him it was “unacceptable behavior,” and asked where his mother was. When McMillan walked away, they chased him on ATVs, jumped out, pinned him to the ground and arrested him. According to police reports, McMillan “attempted to pull his arm away, stating, 'Man, don't touch me like I did something.'"

[AlterNet]