Here's little bro Jake Paul beating the snot out of one his sparring partners ahead of his huge fight with KSI's little bro, Deji, on August 25.

Paul hits him with a few body shots, then a few head shots, and finishes him in a tangled mess in the ropes.

You can see Jake's big bro, Logan, watching the session from outside the ring -- and loving it.

A couple of guys who were at the house rushed over to help the sparring partner. If they REALLY wanted to help, they woulda taught him how to counterpunch.

By the way ... the ring is in Jake's living room -- 'cause he's THAT serious about winning in the YouTube stars' tilt later this month.

Remember ... TMZ Sports also got video of Logan putting a beating on his sparring partner during a training sesh back in June when he put the guy on his ass with a solid left hook.