This is the first rape scene from controversial movie I Spit on Your Grave (1978), a cult film which achieved notoriety for featuring many explicit (for the time) sexual assault scenes.
The victim — played by Camille Keaton — is taking a vacation in the country on her own when she attracts the attention of a local mob. These guys pursue and catch her with the intention of allowing one of their number, a slow guy, to lose his virginity to her. They strip off her bikini and hold her down, but he loses his nerve. So the ringleader rapes her instead, ignoring her angry protestations and cumming inside her.
She is allowed to slowly drag herself to her feet and stumble off, dazed and naked, before the gang catch up with her again and repeat the rape, going on to abuse her repeatedly over the next few hours. This sets the backdrop for her revenge and the rest of the movie shows how she sets about exacting her own form of justice against her brutal attackers.