Group sessions are more instructional whereas the Semi-Private is an intense 45-minute workout and technical training session.
If someone needs to learn to kick a ball, we do not have the time to teach 250+ players individually, so we teach the skills in a group model.
If they want a more individualized workout or training session, they would pick a Semi-Private class. This would be to basically perfect a certain technique. LeftFoot has created the Semi-Private model with a 1:4 ratio giving them more one-on-one time.