The stabbing occurred at about 2 a.m. at the Roosevelt station, according to police. Police said a person was being chased by a group of three people.
The person being chased ran behind a CTA employee, 38-year-old ironworker, Michael Gardiner, who was stationed on the platform.
"Screaming and yelling at him, you know, give us the money, swearing," Gardiner described.
Michael Gardiner said when the three didn't relent, the trio grabbed the man.
"They were about to push him on the tracks," Gardiner remembered.
That's when he said he stepped in, throwing one of the men to the ground.
Then Gardiner was stabbed in the chest and stomach as he tried to defuse the situation, police said.
"The second individual who was with him about to throw that guy on the tracks. What I thought was a punch, stabbed me twice," Gardiner described.
Gardiner said he grabbed the knife, the three took off back up the stairs to street level, and that's when he realized he had been stabbed.
"I felt the blood really coming and told coworker of mine, another ironworker, 'we gotta go. I'm losing a lot of blood,'" Gardiner recalled.
One ironworker said when [the suspects] ran back up the stairs the suspects also sprayed mace in the face of another CTA worker.
The suspects fled the scene. The victim was transported by a coworker to Northwestern Memorial Hospital, where he's recovering after undergoing surgery.
Some Red Line riders were on edge on Friday after the attack.
"You can see the tension down there with others. You just wait for something to happen," said Red Line rider Andre Powell. "I'm surprised I haven't seen more things happen down there."
Keith Hill, president of a local chapter of the Amalgamated Transit Union, is sadly unsurprised by the attack. He says the roughly 6,500 bus drivers, mechanics, clerks, janitors and money handlers who his union represents that are employed by the CTA are in constant danger and are frequently the target of violence, despite the presence of security cameras.
"We're attacked daily, whether it's verbal or physically," he said.
Friday night, Guardian Angels kept watch over the Roosevelt red line stop.
"We're not only patrolling but we're handing out information. The small information that is actually out there right now. And we're asking the public that if they have any information, to call the police." Said Michael Fuentes with Guardian Angels.
Hill said a female driver was attacked Thursday, just hours before the incident at the Roosevelt station.
"Her eye socket fractured for requesting a fare. That's part of our job. Why be abused or attacked for doing our job?" Hill said.
Now, Gardiner is in a hospital bed instead of heading back out to work on the tracks.
And despite the attack, he said it could have been worse.
"I would much rather be here than see a guy laying on the tracks. I didn't expect this, but would it prevent me from doing it in the future," he said. "No."
The CTA station and platform are all covered with surveillance cameras, from which police were able to pull photos of the suspects.
Police are investigating. The CTA said it is working closely with police, including providing any available security camera video. No one is in custody.