Thank you for the opportunity to help you with your question!
In ballistic stretching, an individual stretches to the furthest point that they are able to.On the other hand, In static stretching, an individual stretches to the point where they have a feeling of a gentle pull in the belly of their muscle, he/she then holds the position at that feeling. Finally, PNF stretching is where one stretches till they feel a slight discomfort; it is at the point where there is the contraction of the hamstring isometrically, then relaxes after which they slowly deepens the stretches using the quadriceps (opposing muscle).
Please let me know if you need any clarification. I'm always happy to answer your questions.