Badly Injured in Fireworks Explosion

A Lakers fan blew off his hand during a fireworks accident while celebrating the team's NBA championship -- and dramatic video shows an LAPD officer with medical training rushed to his aid.

It all went down in Los Angeles on October 11, when thousands of people took to the streets to celebrate the Lakers' victory over the Miami Heat in the NBA Finals.

One man apparently suffered a Jason Pierre-Paul-style injury -- with a firework blowing up in his left hand.

LAPD Officer Christopher Gonzalez -- a former Army Ranger -- was on shift that night ... and immediately jumped into action.

"In the blink of an eye, the combat veteran becomes the guardian we train our officers to be," the LAPD says in a…