Charges have been dropped against the headmaster of a prep school in an affluent Philadelphia suburb who was accused of assaulting his teen son in a dispute over a cellphone and marijuana.

The Delaware County prosecutor's office tells The Philadelphia Inquirer (http://bit.ly/2eVgUzM) police had probable cause to arrest Haverford headmaster John Nagl but had "insufficient evidence" to pursue a prosecution.

It's unclear what the decision means for Nagl's employment. He was placed on administrative leave after the Oct. 10 altercation.

Police say Nagl told officers he had taken his son's cellphone and marijuana and a physical altercation broke out when he heard his son speaking on the phone. Police say Nagl admitted putting his son in a chokehold.

Nagl's attorney has said parents can use force to protect their child's welfare.

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Information from: The Philadelphia Inquirer, http://www.inquirer.com