Marshawn Lynch ain't one for motivational speaking ... so when he visited his old high school, he decided to throw on some pads and straight WRECK fools at team practice.
'Shawn shared a video of him droppin' sweat with the boys at Oakland Tech -- the place where Beast Mode all began -- and he didn't hold back ... taking on swarms of tacklers and even stiff-arming one kid to hell on his way to the end zone.
No word on when the video was shot -- but we're looking into it.
Lynch won't suit up for the Raiders this week after pushing a ref last Sunday .