The family of boxer Prichard Colon, who suffered a traumatic brain injury during an October 2015 fight, remains hopeful that he will recover and awake from his coma. Attorney Ari Casper says the fight should have been called by the ringside doctor. (1:40)

The parents of former boxer Prichard Colon filed a lawsuit Wednesday seeking more than $50 million from the ringside doctor and promoters connected with the Oct. 17, 2015, bout in Fairfax, Virginia, that left Colon in a persistent vegetative state.

The complaint, which was filed in the Superior Court of the District of Columbia, alleges medical malpractice by Dr. Richard Ashby for failing to act when Colon indicated several times that the back of his head hurt and for not stopping the fight in the seventh round. That is when Colon reportedly told Ashby he was dizzy and had pain in the back of his head after a Terrel Williams rabbit punch sent him to the canvas.

The suit further asserts that co-promoters HeadBangers Boxing and DiBella Entertainment were negligent because they did not provide a physician with necessary qualifications, experience and competence.

"When you hear dizziness and pain in the back of the head after trauma, you send the patient to the hospital," Ari Casper, the Colons' attorney, told Outside the Lines. "As a matter of fact," he added, "there's a heightened cause for alarm because you know he's going to be hit in the head for the remainder of the fight."

Casper said the suit seeks an unspecified amount exceeding $50 million because "the cost of caring for a patient in Prichard's condition is astronomical, he requires around-the-clock care and his pain and suffering is unimaginable."

An aide of Ashby's in his Washington, DC family medical practice told Outside the Lines Wednesday that Ashby has no comment. Lou DiBella, CEO of DiBella Entertainment, said he had not seen the lawsuit and could not comment on it, but that "what happened to Prichard was a tragedy and we are deeply saddened by it." A message left for HeadBangers Promotions has not yet been returned.

On Thursday, the spokesperson for the Virginia Department of Professional and Occupational Regulation -- which regulates boxing in the state, told Outside the Lines the DPOR selects ringside physicians and in 2014 entered into a contract with Ashby. Mary Broz Vaughan said Ashby was assigned by David Holland, executive director of Virginia's boxing program, to the Colon-Williams bout pursuant to state regulations.

Colon, who was born in Florida, left at 14 to pursue boxing in his parents' native Puerto Rico, where he went on to win five amateur titles. Considered a rising star, he had a 16-0 professional record with 13 knockouts before the nationally televised Saturday afternoon match scheduled for 10 rounds against Williams, who entered 14-0. The welterweight fight ended in Colon being disqualified after the ninth, when his cornermen undid his gloves, saying they thought the final round had just been completed.

Prichard Colon's mother, Nieves, cares for him in the Winter Park, Florida, home where she and her ex-husband, Richard, raised him. William Weinbaum/ESPN

Colon had to be helped to the dressing room by his mother, then he vomited and collapsed. He was rushed by ambulance to the hospital, where emergency brain surgery evacuated a subdural hematoma and relieved pressure on his skull. But 1½ years later, at age 24, Colon remains unaware and unresponsive. He is not on a ventilator, but breathing is all he can do on his own.

Colon's mother, Nieves, cares for him in the Winter Park, Florida, home where she and her ex-husband, Richard, raised him.

In recent interviews for SC Reportajes on ESPN Deportes and Outside the Lines on ESPN, Nieves and Richard Colon said they haven't given up on their son regaining some brain function in the years ahead, despite a bleak prognosis.

"The doctors don't give us hope," said Richard, who comes to the house daily to assist with his son's care. "They say that he's got a mark on the CT scan [that] shows like a black spot -- that it's too large for him to recuperate."

Beginning with the first round of their bout at EagleBank Arena, Colon gestured repeatedly toward the back of his head and complained that Williams was striking him there. In the fifth round, Colon had two points deducted for hitting Williams with a low blow that referee Joe Cooper ruled was intentional, after a grimacing Williams went down. And in the sixth, after another low blow by Colon -- who then gestured about being struck by rabbit punches, Cooper called time and warned both fighters against low and behind-the-head shots.

Then, in the seventh, Colon landed on the canvas after taking Williams' overhand right to the back of his head and neck. Cooper again called time, advised Colon he had up to five minutes to recover, and deducted a point from Williams for the illegal blow. After Ashby examined Colon, NBC Sports/Premier Boxing Champions ringside reporter Kenny Rice told the TV audience that Ashby said he concurred with what Colon had said during his exam -- that he could continue to fight despite the dizziness and head pain.

Williams, who taunted Colon with cutthroat gestures in the fifth and seventh rounds, did in the ninth what no other Colon opponent had -- he knocked him down. And he did it a second time before the bell ended what proved to be the last round.

An emotional Nieves Colon recounted her son having his arm around her for support as he struggled to get to the dressing room while fans jeered him for feigning injury. "I said, 'God, please, I don't want my son to hear that,' because my son was not faking, Prichard is not like that."

Virginia's Department of Professional and Occupational Regulation investigated the bout and concluded: "While Colon's medical condition following the contest against Williams is tragic, there is not one action so apparent and/or egregious to justify laying blame to any one person."

But Broz Vaughan, the department spokesperson, acknowledged the DPOR doesn't license or discipline ring doctors and refs. She told Outside the Lines, "It's certainly frustrating for folks who wish we would have been the entity to make the call as to right or wrong; it's a horrible tragedy."

The state inquiry's full interviews with Ashby, Cooper, Williams and others were not made public, and when Outside the Lines requested access, Broz Vaughan said that since the Colons did not agree to be interviewed or provide statements to the DPOR, the case file remains officially open and therefore exempt from disclosure.

The DPOR report said medical evaluation methods used during a fight are the "sole responsibility" of the doctor and are presumed to be in accordance with established standards of care.

Prichard Colon's father, Richard, who trained him in childhood boxing sessions in the garage, now takes his son for rides in a wheelchair and reads to him daily. William Weinbaum/ESPN

John Stiller, chief physician and neurologist for the Maryland State Athletic Commission, who said he saw the fight live on TV and recently reviewed a recording of the telecast, told Outside the Lines, "The fight should have been stopped at that moment [in the seventh round], and I still cannot think of a medically sound reason it wasn't.

"The combination of receiving a blow or blows to the head resulting in a boxer complaining of headache and dizziness requires an immediate stoppage," he said, adding that stopping a bout can be a difficult decision, but not in this instance.

The Colons' lawsuit contends that Ashby didn't have the requisite background to adequately safeguard the fighters and, because he also works as a boxing promoter, there was a conflict of interest and his judgment as a ring doctor was compromised. The suit says the promoters of the bout were responsible for ensuring the safety of the fighters, including thorough adherence to a proper protocol for handling potential brain injuries. Boxing, which has no national governing body, does not have an industry-wide traumatic brain injury protocol.

Said Dr. Stiller: "There is a basic tenet that a physician first rules out and treats medical conditions that if not diagnosed and addressed quickly may lead to death or permanent disability." A seventh-round stoppage, he said, would have given Colon "the best chance to limit the evolving injury," but that the fight's continuation subjected him to further blows to the head.

Virginia's investigative report noted that Holland, head of the state's boxing program, said referee Cooper could have been more aggressive in trying to prevent the fight from becoming foul-plagued.

Asked by Outside the Lines about electing against suing Cooper or any other parties on behalf of the Colons, Casper said, "All I will say at this point is that we are continuing to carefully analyze the responsibilities and legal duties of all participants in that tragic event."

The undefeated Williams, now 33, has not fought since the 2015 bout with Colon. He said days after the fight that he had been praying for Colon. Messages left by Outside the Lines in recent months requesting interviews with Williams and his trainer, Joe Goossen, have not been returned.

Meanwhile, Colon is bedridden in his mother's house. His father, Richard, who trained him in childhood boxing sessions in the garage, now takes his son for rides nearby in a wheelchair and reads to him in the hope that at some point, somehow, something will register.

And Colon's mother, Nieves, shared through tears the wish that helps sustain her.

"My dream, my hope, my faith is to see God put his hand over my son and he can wake up."

ESPN's Fernando Calderon contributed to this report.