Eight-time world champion Floyd Mayweather has left HBO in favor of a 30-month, six-fight deal with Showtime and its parent company CBS in what is being called the richest pact in boxing history.Financial terms of the deal between the undefeated boxer and Showtime/CBS, announced in a statement by Mayweather Promotions, were not disclosed.In making the announcement, Mayweather also confirmed a May 4 fight with Robert Guerrero which will mark the fighter’s Showtime debut.Widely recognized as boxing’s top pound-for-pound fighter, Mayweather (43-0, 26 KOs) has been a part of boxing’s four biggest non-heavyweight pay-per-view events.The 35-year-old fighter was listed as the highest paid athlete in 2012 by Forbes after earning $85 million from two fights against Victor Ortiz and Miguel Cotto. Filipino southpaw Manny Pacquiao ranked second with earnings of $62 million.According to the statement, Mayweather averages more than 1 million pay-per-view buys per event, the highest of any boxer, and if all six fights take place it could result in the richest individual athlete deal in all of sports.Agencies