Hernandez was meant to be playing in the final for her team Azzuri Cachorros U11s in a Springfield Soccer Club girls tournament before organisers said she couldn't take part.
As a result, her whole team was kicked out of the tournament too.
Her father, Gerardo Hernandez, told local TV station WOWT 6 News that his daughter "was in shock".
Mili added: "Just because I look like a boy doesn't mean I am a boy. They don't have a reason to kick the whole club out."
Despite showing Mili's insurance card to the organisers, they did not change their minds. Former U.S. women's national team stars Abby Wambach and Mia Hamm offered their support to Hernandez on social media, as did legendary female tennis player Billie Jean King and a large section of the U.S. soccer community.
Just to make themselves even more unpopular, the Springfield Soccer Association have reportedly said the disqualification was not because of Hernandez's short hair, but because she is mistakenly listed as a boy on the teamsheet, which "is a violation of state and tournament rules".
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