Dodgeball With Tom Brady's Fam??

... 'I Was Scared!'

Dodgeball with Tom Brady and his softball-playing sisters was exactly what it appeared to be -- TERRIFYING!!!!!!!!!!!!!

This according to Gisele ... who took part in the summer "fun" -- where Tom famously got so competitive in the children's game -- he chucked a fastball at his own mother!!

Brady's supermodel wife went on "The Tonight Show Starring Jimmy Fallon" on Thursday to explain exactly how savage football's G.O.A.T. and his fam get when they square up on the court ... and yeah, she says it's as aggressive as it looked.

"They're pretty strong," Gisele said of Brady's sisters. "They were softball players. They're intense!! I was scared ..."

Gisele says the rubber-ball…