Philadelphia Police have released surveillance video of a suspect attacking a 23-year-old man on a SEPTA train in an attempt to rob him of a phone.

Passengers rushed in to help the victim. It's not clear if the incident was a case of a so-called 'knockout' attack some media are reporting as a trend, or a robbery gone violent.

According to police, the attack occurred 8:30 a.m., Oct. 30 when the victim was on the Frankford Elevated train traveling toward 69th Street.  He noticed a nearby man acting suspicious.

As the train approached the Berks Street station, the suspect suddenly lurched at the victim,  punching him in the face demanding his cell phone.  Passengers rushed in to help, but the suspect fled the train at the Berks Street stop.

The victim received a cut lip and facial swelling.

The suspect is described as a bearded black male, about 5'11", with a dark complexion and slim build. He wore a two-tone gray jacket, with tan corduroy pants, black or gray Nike sneakers and a black skull cap.

The attack is similar to what's being report as part of a so-called 'knockout' game trend, whereby innocent bystanders are attacked from behind.  But it's unclear if the trend even exists.  Police say they are examining recent video clips of such attacks to make a determination.

The knockout attacks are similar to a spate of reports in 2010 of a kids' game called "Catch and Wreck," in which unsuspecting adults were beaten for fun.  Now, however, more such incidents are being caught on mobile phone and surveillance videos.

In this latest incident, however, the motive appears to be robbery. Anyone with information on the SEPTA attack should either:

-Call 911

-Submit a tip via telephone at 215.686.TIPS (8477)

-Text a tip to PPD TIP or 773847.

-Or use this electronic form to submit a tip anonymously.