Sullivan made his first MLS appearance in July, becoming the youngest debutant in major U.S. sports history in the process. He was youngest player to ever play in the league by smashing Freddy Adu's youth age record.
“It was like… I've never been on the field with noise like that,” Sullivan told GOAL earlier this summer. "Obviously, I've been to European Games where the stands are cool and all, but especially hearing it ... it was pretty cool. And having my name being the chant was even better.”