The size of the ball weighs 7kg in men's competitions and 4kg in women's competition.
Roser was rushed by ambulance to the nearby Good Samaritan Hospital in Downers Grove, where he was pronounced dead.
"Wheaton College is grieved by the tragic death of freshman Ethan Roser," a statement from the college said.
"Roser, a 19-year-old freshman transfer student from Cincinnati, Ohio, was volunteering at a Wheaton College track and field competition, where he was accidentally struck by a hammer during the hammer throw event."
"We are deeply grieved, but, because of our faith in Christ, not without hope," said Wheaton College President Philip Ryken.
"We ask people to pray for Ethan's family, his friends, and our campus community."
According to the Chicago Tribune, Roser was the son of Christian missionaries who spent his early years in Africa and was studying to be a minister.
"We are in shock and struggling to comprehend how we will live without him," his brother Ethan wrote on Facebook.