José Luis Castillo vs. Floyd Mayweather Jr., billed as Clash of the Champions, was a professional boxing match contested on April 20, 2002, for the WBC and The Ring lightweight titles.

[1] Immediately following his eighth successful title defense over Jesús Chávez in November 2001, reigning WBC super featherweight champion Floyd Mayweather Jr. announced that after 27 fights in the division, the Chávez fight would be his last as a super featherweight and he would be moving up to lightweight to challenge the WBC lightweight champion José Luis Castillo.

[2] Though he was coming into his first fight at lightweight, Mayweather, ranked as one of the best pound-for-pound fighter, was a 5–1 favorite over Castillo.

However, Mayweather ran into trouble in the month preceding the fight when he was convicted on two counts of domestic violence though he accepted a plea bargain and was given a suspended sentence, avoiding prison and allowing him to go through with his fight with Castillo.

However, in the sixth round, Castillo fought aggressively and was finally able to get to Mayweather and landed clean shots to the head and body from then on.