As a trainer, Mayweather preaches defense and a stiff jab. He teaches many of his boxers a defensive technique known as the shoulder roll, in which the fighter uses his front shoulder to deflect blows and limit their impact. He has on many occasions, including HBO's Mayweather-Hatton 24/7, claimed to be "Floyd Joy Mayweather Sr., 'The Greatest Trainer of All Time'".
He is the former trainer of top light heavyweight Chad Dawson, former 2 division champion Joan Guzmán and women's champion Laila Ali. He is well-known for his stint as Oscar De La Hoya's trainer from 2001 through 2006. He said he would train De La Hoya for his May 5, 2007, fight against his son, but demanded a $2 million fee to do so. After considerable deliberation, De La Hoya opted not to hire Mayweather Sr. and announced on Jan. 30, 2007, he would use Freddie Roach instead.
The snub briefly reunited father and son, with Floyd Sr. turning up at the Mayweather Jr. boxing gym, while Roger (who had been banned from being in the corner at boxing matches for 12 months for starting a riot during Floyd Jr's bout against Zab Judah last year when he attacked Judah) served six months in jail for a domestic assault. But when Roger was released, the situation became awkward because of the brothers’ rivalry. He also spent 5 years in Federal prison for convictions for violating Drug Trafficking laws.
Floyd Jr. chose Roger as his trainer and Floyd Sr. left again, claiming that the father-son relationship was "back to square one" for choosing Roger over his own father again. Floyd Sr. agreed to once again train De La Hoya in anticipation for Mayweather Jr. – De La Hoya II presented by Golden Boy Promotions. However due to disagreements with how revenues would be divided amongst the two fighters, the bout was cancelled. Mayweather Sr. trained Manchester's Ricky Hatton for seven weeks prior to his bout against Paulie Malignaggi on 22 November 2008 at the MGM Grand in Las Vegas.
Hatton retained his IBO light welterweight title with a technical knockout in the 11th round. However, Hatton lost only his second fight under Mayweather Sr with a second round knockout by boxing legend Manny Pacquiao. The famous feud between Floyd Mayweather Sr. and Floyd Mayweather Jr. finally came to an end as father and son made up before Jr's return to the ring after a 21- month lay off. However Jr's uncle Roger Mayweather still trains Jr.. On the HBO 24/7 program Floyd Mayweather Sr. was quoted as saying 'I don't need to train my son, I need a relationship with my son."
A proposed March, 2010 fight between Mayweather Jr. and Manny Pacquiao fell by the wayside in January, 2010 when the camps representing both fighters could not agree on a timeline for drug testing for the fight. A more stringent drug test was sought out by Mayweather Jr.'s representatives due to inadequacies in the current testing standards and a suspicion that Pacquiao might be utilizing banned performance enhancers in his training regimen. Mayweather Sr. had been very vocal about his theory that Manny Pacquiao's impressive displays as a welterweight were aided by performance enhancing drugs for several months prior to the negotiation for a fight between his son and Pacquiao. On March 21, 2011, U.S. District Judge Larry Hicks said Pacquiao has sufficient evidence to continue his lawsuit that alleges Floyd Sr., Jr., and Roger acted with malice by accusing the Filipino boxer, and as of December 2011 Jr had been deposed and the case was continuing seeking damages of $10 million.
Mayweather trained UFC fighter BJ Penn for two weeks. Mayweather helped improve Penn's boxing skills, who many consider to be amongst the best in mixed martial arts. Mayweather said that he taught Penn not to be so aggressive.
