Rams fan Lita Abella made the allegations in a lawsuit -- obtained by TMZ Sports -- claiming she missed the rest of the game due to an incident in the third quarter.

In the docs, Abella claims she was sitting in her seat when she "suddenly, and without warning," felt a forcible blow to the back of her head.

Abella says the impact was so strong, it forced her out of her assigned seat and sent her flying into the back of another seat rows ahead.

In the suit, the woman alleges that a man lost his balance and fell after "high fiving" another man ... causing him to fall into where Abella had been sitting, which resulted in her face and head colliding with another seat.

The woman says she suffered gnarly injuries -- including a concussion, orbital fracture, fractured nose, and fractured shoulder -- and ended up missing the trophy ceremony because she was in the hospital.

Abella is accusing SoFi Stadium of negligence and premises liability -- saying the stadium was ultimately responsible for what she describes as the "dangerous and defectively planned" seating which led to her injuries.

She's suing for unspecified damages.