Could this be an acl tear or something else?

this weekend (saturday) i was playing softball and my legs were straight up and a girl slid right into my knee with her foot still in the air and i heard it pop, and i dropped to the ground . it started to swell and it hurt to straighten or bend it . now i can straighten it way better than bend it and there is still a lot of pain and if i move to the side it feels like its gona give out . and it hurts on the left side of my right knee .. it is still swollen a little. does anyone know if this is an acl tear?