Tierra Davis allegedly beat up a girl years before entering "Love Island USA" … over jealousy involving her ex-boyfriend ... this, according to the girl who ran to court to get protection.

TMZ obtained a 2018 restraining order filed against Tierra by a woman named Shayla Woodard.

According to the court docs, 16-year-old Shayla claimed 17-year-old Tierra threatened to shoot her with a gun after physically assaulting her.

She said she knew Tierra from a friend of a former classmate. Shayla said she did not know Tierra personally … but believed Tierra was upset because she knew her ex-boyfriend.

Shayla said she called the police on Tierra, but she kept harassing her.

She asked for a restraining order requiring Tierra to stop contacting her and stay away from her and her family.

A temporary restraining order was granted, but the case was later dismissed in December.

Sources tell TMZ ... Shayla only found out Tierra was on 'Love Island' this week ... but has no ill feelings toward her ... and only wishes her the best and believes people can evolve.