Tennacity is a brand that offers an online course and book called Tennacity: The Tenacious Mindset, On & Off the Court. This course is designed to help individuals develop a strong mental game in tennis, based on the experiences of Angelo and Ettore Rossetti, who set a Guinness World Records™ title by keeping a ball in play for 15 hours. The course emphasizes the importance of mental skills education and provides practical tips and strategies to enhance one's mindset both on and off the court.

The brand has garnered praise from renowned figures in the tennis world. Nick Bollettieri, founder of the IMG Academy, commends the dedication of the Rossetti twins and praises the insightful content of the book. Wayne Bryan, coach and father of the Bryan Brothers, highlights the valuable insights and information that make the book a valuable resource.

Jeff Salzenstein, former Top 100 ATP singles and doubles player, highly recommends the book for athletes and coaches, praising Angelo's favorite strategy of controlling the controllables. Overall, Tennacity offers a comprehensive approach to developing a tenacious mindset in tennis, backed by real-life experiences and expert endorsements