An attorney for the Haverford School headmaster who was placed on leave this week after a charge of simple assault against his son said Thursday that his client is innocent and vowed to try to get the charge dropped.

The allegations against John A. Nagl, 50, are a "private family matter" and one that Nagl "feels really bad about," said the Haverford-based attorney, Robert Keller.

"He loves his son, and now his son's misdeeds have been broadcast in the news media," Keller said in a phone interview. "He was a very protective father who was trying to help his son."

On Monday, according to court documents, Nagl, of Haverford, was arrested and charged with simple assault - a third-degree misdemeanor punishable by up to one year in prison - after an altercation with his 15-year-old son emerged at his Haverford home.

Court documents gave the following account:

On Saturday, Nagl found marijuana in his son's backpack, and he confiscated the drugs, along with his son's cellphone, as punishment.

But the next day, Nagl discovered that the drugs and phone were gone, and on Monday overheard his son - a student at the Haverford School - using the phone in a bathroom of the home. When Nagl attempted to take the phone back, his son refused - forcing Nagl to take it physically from his son's hands. At that point, as Nagl walked away, his son "re-engaged in a physical altercation over the phone."

Nagl, according to the documents, told police "he put his son in a choke hold to end the altercation quickly." Nagl's son called 911.

When Haverford police arrived, they found a "visible red mark on [his son's] chest below the neck line," and the son told police he felt "light-headed."

Nagl was arraigned Monday and released on $30,000 bail. Soon after, Haverford School announced that Nagl had been placed on administrative leave, which Keller said is paid.

"He does not want his son involved in the use of drugs," Keller said Thursday. "The irony is that the protective father is now arrested and his career is now in the balance. It just does not seem appropriate."

According to his LinkedIn entry, Nagl has been headmaster at the school for three years. He is a retired Army officer with combat experience in Operation Desert Storm during the Gulf War and Operation Iraqi Freedom. An expert in counterinsurgency, he earned his master's and doctorate degrees from Oxford University, where he studied as a Rhodes scholar, according to the Haverford School website.

With Nagl's preliminary hearing more than a month away, Keller said he and Nagl will soon meet with the board of trustees with "the hope that they will let him come back," Keller said.

And, he said, they have been talking with the Delaware County District Attorney's Office in an attempt to persuade officials to withdraw the case - maintaining that Nagl is protected under a provision of the law that allows a parent to use force justifiably for the purpose of "safeguarding" the "welfare of the minor," including through "punishment of his misconduct," Keller said.

A spokeswoman for the District Attorney's Office said the matter was under review.