The Boston Globe reported that four of the victims were listed in critical condition.
Despite the danger, spectators scrambled to assist those injured by the lightning strike. Hector Rivera, an Air Force reservist, was among those who rushed to help.
"People were falling like bricks," Rivera told the Boston Herald. "It looked like a movie scene. We kept hearing thunder. You could hear people crying."
Boston EMS officials say the victims were taken to various hospitals after Sunday's incident with burns consistent with a lightning strike. The youngest victim was 13 years old, while the oldest was in his 40s.
The storm struck at about 3:30 p.m. during a soccer game at Dorchester's Franklin Field.
EMS deputy supervisor Michael Bosse said he could not remember 10 people being struck by lightning at once.