USC announced their official practice admittance policy:

Admittance to USC football team practices on campus will be restricted to pre-approved guests who submit requests 24 hours in advance, according to a policy released today by the USC athletic department.

Those eligible to attend practices if pre-approved are parents, guardians, spouses and siblings of current players, as well as a limited number of guests escorted by certain USC administrators. Additional limited exceptions (such as other relatives of players) may be made with the pre-authorization of a Senior Associate Athletic Director.

Those who are pre-authorized to attend practices may only have contact with coaches and athletic department personnel.

Among those not permitted access to practice are agents (such as athlete agents, marketing agents or financial advisors to athletes) or their employees, representatives or affiliates.

Unless you are a relative or know a very important person, you will not be able to attend practice.

Practice admittance policy [uscripsit]