New video obtained by TMZ Sports shows all of the drama that led up to an intense conversation between Marshawn Lynch and football camp moms ... and everything started with a hitting drill.
At Lynch's Fam 1st Family camp in the Seattle area on July 28 ... Lynch had the kids -- some as young as 9 years old -- line up to hit each other without pads.
The exercise got pretty violent, with several kids hitting each other hard ... and throwing each other to the ground.
It appears at some point during the drill, some of the kids had objections toward the workout .