A legal defense is any reason that the law recognizes as a valid reason for not granting the eviction. In some cases there are no legal defenses. But in many cases there are if you know where to look.
The video you watched mentioned a few common defenses, which are
(1) You did not do what the landlord says you did,
(2) You did what the landlord says you did but that does not count as a breach of the lease
(3) You did what the landlord says you did and what you did breached the lease, but it’s really minor and not a "material" breach; and
(4) The landlord did not give you all required notices. In South Carolina, a landlord's failure to give a proper notice usually is a solid defense to an eviction. You should always assert lack of a required notice if the landlord has failed to give a proper notice to terminate the lease.
Another common defense is what the law calls "waiver." Even if you breach you lease, the landlord can "waive" that breach by not taking steps to terminate your lease, telling you not to worry about the breach, or doing or saying something to indicate that the landlord is letting that breach slide, such as by continuing to accept your rent without calling out the lease violation. If the landlord "waives" a breach, the law says that the landlord cannot later use that breach to terminate your lease.
EXAMPLE: Assume that your lease says you cannot have other people living with you who have not been approved by the landlord. Your friend moves in and has not been approved by the landlord. If the landlord finds out about that and lets it go for a while without saying anything and continues accepting your rent, the landlord is waiving that breach. If your friend later moves out, the landlord cannot terminate your lease, say, a month after your friend moves out if the landlord knew your friend was living there and permitted him to live there. A slightly different rule applies for on-going breaches of the lease. Assume your friend did not move out but continues to live in your unit. Even though your landlord has waived that breach for a period of time, the landlord has the right to stop waiving the breach and require your friend to leave. The landlord stops waiving the breach by giving you fair warning in the form of a 14-day notice to have your friend leave the dwelling unit.