Here's Lakers rookie Kyle Kuzma serving notice to the rest of the NBA not to try him ... getting a lesson in the pugilistic arts from one of the most famous boxing trainers in the country.

Kuzma -- one of the Lakers summer league standouts -- headed over to the Team Watson Boxing Club in L.A., the city's new boxing hub, where champions like Leo Santa Cruz work out.

The lesson looks pretty intense (kid's got power) ... and it's definitely legit training 'cause the guy holding the mitts is Phil Paolina, an ex-fighter whose worked with celebs like J.Lo and even Bob Dylan.

Careful Kyle, those hands are for shootin' not for fightin'.