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.