Greenwood was a walk on freshman and ended up starting for the Hawkeyes for three seasons. He played 2011 NFL pre season with the Pittsburgh Steelers before being cut from the squad before the beginning of the 2011-12 season.
On Friday afternoon, September 9, 2011, Greenwood was working out on the football field of his former high school (Pleasant Valley High School of Bettendorf, IA), when he collapsed from a heart arrhythmia. When attempts to resuscitate him failed, he was rushed to Trinity Medical Center of Bettendorf, before being airlifted to University of Iowa Hospitals and Clinics. Although he survived the episode, it caused serious neurological injuries. As of July 2012, he is still recovering from his injuries, receiving physical therapy five days per week.
For the Iowa Hawkeye football game on September 24, 2011, against Louisiana-Monroe, attending fans were encouraged to wear green for a "green-out", in honor of the former standout.
The Brett Greenwood Foundation has been established to provide a donation fund that will be used to support the University of Iowa Hospitals and Clinics, as well as the Hawkeye Athletics Department in the form of an Endowed Scholarship in Brett's name.