A 23-year-old New York father who police say pulled a knife on another man and threatened to kill him in front of his family on board a subway train after the latter criticised him for striking his own son broke down in tears before a judge on Wednesday.

Edgar Rodriguez, of Roosevelt Island, was arrested on Tuesday on charges of endangering the welfare of a child, menacing and criminal possession of a weapon, the Daily Mail reported.

Rodriguez was caught on video boasting that he was 'tough' after allegedly hitting his toddler son. Photo / Supplied
Rodriguez was caught on video boasting that he was 'tough' after allegedly hitting his toddler son. Photo / Supplied

During his arraignment on Wednesday, Rodriguez, who boasted in a now-viral cellphone video that he was "tough", appeared dejected and had tears rolling down his face as his lawyer addressed the judge.

Rodriguez was ordered held on US$2000 bail and barred from having any contact with his son. Prosecutors asked the judge to set his bail at US$10,000.

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News cameras were rolling on Tuesday as police officers led Rodriguez, dressed in a brown shirt, out of the station and into the back of an awaiting car, reported NBC New York.

The suspect, who appeared slightly different than in the cellphone video from the subway, having apparently gotten a haircut and a shave, made no statements to the press.

Rodriguez's arrest took place nearly three weeks after the altercation on board a northbound E train, but just one day after the NYPD released footage showing the suspect threatening the victim.

The incident took place at around 3.30pm on June 24 on board a northbound E train after the victim confronted the suspect about how he was treating his own child.

The train was pulling into West 4th Street station when the suspect, described only as a black man in his 20s, reportedly hit his crying son on the arm.

A fellow straphanger, a 45-year-old man traveling with his wife and their four-year-old daughter to get ice cream, told the younger dad, 'You shouldn't do that.'

The Good Samaritan's well-meaning comment prompted the suspect to unleash a foul-mouthed tirade at him.

The portion of the recording released by the NYPD does not show the slap but starts with the suspect yelling at the other rider, "I'm tough by myself, bro."

"Why are you hitting your son?" the older dad asks him, to which the suspect replies: "Cause he's my son and I can do that."

The suspect then proceeds to goad the man who dared criticize his parenting style, telling him, "Come, do something… I will kill you. I want you to do something."

He also issues a threat to the older man: "I will change your f***ing life on this train."

After raving and hurling expletives for a full minute, the suspect called his own toddler son a "f***".

The married dad later tried to calm his terrified, sobbing daughter by reassuring her that "it's going to be okay".

Rodriguez was caught on video threatening a married dad with a knife and hurling expletives at him on the E train. Photo / Supplied
Rodriguez was caught on video threatening a married dad with a knife and hurling expletives at him on the E train. Photo / Supplied
The 23-year-old dad launched a furious tirade at a 45-year-old man. Photo / Supplied
The 23-year-old dad launched a furious tirade at a 45-year-old man. Photo / Supplied

In the cellphone video recorded by the victim's wife, the suspect tells him, "Yeah, tell her it's fine. Your daddy will get killed on this train, n*****."

After the train came to a stop at the station and the doors opened, the man pushed his son's stroller onto the platform and held the doors open.

He then pulled out a small knife and demanded that the married dad step outside with him.

"Come off the train, bro, come on, come one, come on," he tells the other man in the video while waving the weapon.

The Good Samaritan tells the suspect he was just trying to protect his kid, to which the knife-wielding thug says, "I don't give a f***. Come out here, come out here, bro."

The victim warns him he will call the police, but the suspect responds to the threat by saying he does not care, grabbing his privates and spitting on the family through the open doors.

In an interview with CBS New York, the victim, who did not wish to give his name for fear of retaliation, said he takes the E train daily and is concerned for his safety.