A Muni patron is in the hospital this morning, following a bloody altercation on the back of a Muni bus.

According to San Francisco Police Department spokesperson Sergeant Michael Andraychak, at 1:30 this morning two men —one aged around 25, the other 40 — were riding Muni's 14 line near Mission and Ninth Streets.

The duo "had some type of interaction," Andraychak says, and the younger man threatened to stab the older according to SFPD's report on the incident.

Both men walked to the rear of the bus, where the younger man made good on his threat and stabbed the older man in the torso.

He then fled the bus, Andraychak says, in an unknown direction and hasn't been seen since.

The 40-year-old man was transported to San Francisco General Hospital with a laceration to the rib that police say is non-life-threatening.

The suspect remains at large. According to Andraychak, "it's too early in the investigation to consider releasing video from the bus," but he urges anyone who might know more about this dangerous dispute to call SFPD's anonymous tip line at 415-575-4444 or to text a tip to TIP411, just remember to begin the message with "SFPD."