Final answer:
The claim that Signal 18 is used for all free kick infractions except encroachment of the neutral zone is false, as there are specific hand signals for different infractions in American football.
Step-by-step explanation:
The statement that the signal for free kick infractions, other than encroachment of the neutral zone, is Signal 18 is false. In American football, officials use a series of hand signals to communicate various penalties and calls on the field. Each signal has a specific number and meaning associated with it. While Signal 18 is used for a specific type of infraction, it is not universally applied to all free kick infractions. The actual signals for various infractions can differ based on the specific rules of the football league (NFL, NCAA, high school), and it is important for players, coaches, referees, and fans to understand these differences.