A video of SEPTA police attempting to handcuff a man who is holding a small child has prompted an internal affairs investigaton, the transit agency's top cop said Friday.

In the video, first posted to Facebook, police are seen asking Ellis Smith, 20, to leave the train car. On the platform, police try to place his hands behind his back. The crowd, which remained peaceful, became agitated, because Smith was holding a small child at the time. 

The woman that originally posted the video claimed Smith had paid his fare, but was under investigation because he failed to do so for his child. That turned out to be untrue, police said. The child was too young to have to pay a fare. 

Outrcy over the Facebook video prompted SEPTA police to review surveillance video of the incident. In surveillance footage from the train, a 16-year veteran of the force can be seen shoving Smith by the throat into a wall as he held the child. 

Police say that the officer was afraid he would be disciplined if he backed down and did not arrest Smith.

The incident had the transit agency's top cop taking responsibility.

"If a 16-year officer thinks they can't step away from a situation that's spiraling into something that might jeopardize the safety of a child, that's on me. I never want a child's safety to be jeopardized," Chief Thomas Nestel told reporters at a Friday afternoon news conference.

Hundreds of people have watched the video, shot by G. Ahmad Najam, and posted to Facebook by on Thursday by a woman identifying herself as Irize Refined Earth.

She wrote: "I wish they would put hands on me while holding my kids!!! This police 'entitlement' mentality, which often leads to brutality, has got to stop!"

Smith was charged with disorderly conduct, resisting arrest and fare evasion, said Jerri Williams, SEPTA's spokeswoman. 

Nestel is very active on social media, and often tweets surveillance video of fare dodging arrests under the hashtag #cheesesandwhich, a reference to meals given to incarcerated people. 

At Friday's briefing, he brushed aside some questions about Smith's conduct.

"This isn't about him, this is about us," Nestel said. "I'm not going to change how somebody in the public deals with police. I have to deal with how police deal with the public." 

In April 2013, SEPTA issued a memo to employees urging them not to confront people who did not have the means to pay. Many people have interpreted this to mean that transit operators will allow people to allow for free, Williams said. That memo, however, was issued in an effort to prevent assaults on operators, who may still call the police on people who refuse to pay.

Nestel said that for the past year, his agency has focused on fare evasion. That has lead to a 30 percent decrease in serious crimes.