The victim believes it started as some kind of prank.

PORTLAND, Ore. — A Portland father is warning others after he says his son was attacked by a stranger on the MAX.

Adam Giard said his 20-year-old son was on his way home from work on Thursday night when someone hopped on the MAX at the Northeast 82nd Avenue stop and punched him in the face.

He has asked KGW not to use his son’s name, but described what happened.

Transit police and Portland police are investigating, according to TriMet.

“As the train pulled up to the stop, doors open, my son is sitting there reading his phone, suspect jumped onto the MAX, ran past my son, hit him in the face and then exited the train,” Giard explained.

The attack started on the train but continued when his son followed the suspect off the train at the Northeast 82nd Avenue station, according to Giard.

“Not really knowing what was going on, my son exited the train after the suspect,” Giard said. “At that point, the train pulls away from the station. The suspect continues to assault my son and actually pushes him down onto the MAX track. So, he sustained some injuries there.”

His son managed to go up the stairs on to the bus stop platform to look for help, but was hit again after he was caught taking a picture of the suspect on his phone, Giard said.

“One of the suspects came at him and severely assaulted him. We believe that is when his broken jaw actually happened,” Giard said.

He said the suspect was with another man and a woman, but were not involved in the assault.

His son’s jaw was fractured and had to have surgery. His jaw is now wired shut for at least a month.

“It is absolutely infuriating to me that my child goes to work all day, he works a full-time job, great kid, all he wants to do is come home and enjoy his evening and he can't now and he won't for the foreseeable future,” Giard said. “I mean he has to deal with the consequences of this long term.”

Long term consequences from a random attack, he thinks started as some kind of prank.

“I don't want to see anybody else get injured,” Giard said. “I don't want to see anybody lose their children over something as stupid as a prank or a challenge from somebody's friends. I can't stomach that.”

Giard and his son are now working with police to figure out who did this. They have posted a photo taken by his son of the suspect online and have a possible person of interest. He estimates the suspect is 18 to 20-years-old. There haven’t been any arrests.

The family started a GoFundMe to help with medical bills and said recovering from this will won't be easy.