Arguments that often carry weight
Defense usually begins with likelihood of confusion. Shared words are not enough; courts look at how the marks appear and sound as a whole, how the goods are sold, and who buys them. A term used descriptively, to describe a feature of your product rather than as a brand, may be protected as fair use. If you began using the mark before the plaintiff in your area, you may have rights of your own. Weakness of the plaintiff's mark, for instance where many businesses use similar terms for related goods, can also narrow its reach.
Counterclaims and the Board
A defendant can often ask the court to cancel the plaintiff's registration, on grounds such as abandonment or priority, as a counterclaim. When a civil action and a Board proceeding involve the same marks, the Board usually suspends its case while the court resolves the overlapping issues, because the court's decision may be dispositive. That makes the choice of where to raise each argument significant. Insurance is worth checking: some commercial policies respond to certain trademark or trade dress claims arising from advertising, while many exclude trademark infringement, and coverage turns on the policy language and the allegations.
Building the defense
Collect evidence of your first use, your sales history and regions, examples of your branding over time, any clearance search done before adoption, and communications with the plaintiff. Preserve documents and avoid changing your branding without discussing it first, since abrupt changes can be read in different ways. Answer deadlines in both court and the Board are short. A first meeting usually produces an early view of the confusion arguments, any prior-use rights, the role of insurance, and whether settlement through coexistence or a transition is worth exploring. If the plaintiff is a much larger company, an early and accurate picture of your exposure helps keep settlement discussions grounded.
