Floyd Mayweather -- Gives Boxing Gloves to Leah Still ... To Beat Up Cancer!!!

Pretty cool moment from Floyd Mayweather ... when he hooked up Leah Still with an autographed pair of boxing gloves to help her KNOCK OUT cancer!!

The backstory is interesting ... Leah's dad Devon Still says he's been advising his daughter to approach the cancer fight like Mayweather approaches his opponents in the ring.

"When she was diagnosed with cancer I told her she had to win every round (like boxers- mayweather to be exact) of chemo/treatment and she would win the fight against cancer."'

When Mayweather's camp got word -- he wanted to help ... and according to Devon, "He surprised Leah with an autographed glove for winning her fight and he threw in another glove for me to auction off at my first annual Still Strong Foundation Gala!"

Nice work, Floyd