My professor usually combines class lecture with a group discussion. Can I record this group discussion?

No. The definition of class lecture does not include other classroom activities such as class discussions, unless those discussions are incidental to, and incorporated within, a class lecture. A class lecture also does not include student presentations (whether individually or part of a group), lab sessions, clinical presentations such as patient history, academic exercises involving student participation, test or examination administrations, field trips, or private conversations during a class session. These activities may not be recorded without the express consent of all participants. Your faculty member or instructor may or may not announce when the lecture portion of a class has ended, but it is up to you to ensure that you do not record at an impermissible time.