Thanks very much. Now, into the investigation that left a former football player hospitalized, punched and kicked in the head Sunday morning. One suspect arrested. And this morning, police are looking... See More
Thanks very much. Now, into the investigation that left a former football player hospitalized, punched and kicked in the head Sunday morning. One suspect arrested. And this morning, police are looking at surveillance video, hoping to find the second one. ABC's Alex Perez has the story. Reporter: This weekend, he was celebrating his college graduation. But this morning, former Minnesota university football linebacker Isaac Kolstad is fighting to stay alive. He is in critical condition, suffering severe head injuries, after an altercation with Phillip Nelson. A former star quarterback at the university of Minnesota, named Mr. Football in 2011, before transferring to Rutgers earlier this year. Nelson was arrested and charged with assaulting Kolstad and released overnight after posting bail. This morning, police are on the hunt, looking for a second suspect. The man seen here in this newly-released surveillance video, in a red shirt, running down the street. Described as a white male in his early 20s, wearing a red t-shirt it appears. Reporter: Kolstad and Nelson crossed paths after a night at the bars in man Kato, Minnesota. Striking Nelson in the back, and then walked away. That's when investigators say the man in the red shirt ran up to Kolstad and punched him in the face. So hard, witnesses say Kolstad immediately collapsed. I can hear the sound when his head hit the ground. It was horrible. Reporter: Surveillance cameras captured Nelson approaching Kolstad, kicking him in the head. Right now, he's been unresponsible for about ten minutes. Reporter: Nelson told police, he doesn't remember kicking Kolstad. And rudd Rutgers is reserving comment until the legal process is complete. Kolstad's family has already been told he will have permanent brain damage. But the extent of the damage won't be known for a few weeks.
This transcript has been automatically generated and may not be 100% accurate.