Do I remember right that kinetic energy is mass * velocity squared?
Not sure if billiard balls or similar ideal objects make a good comparison. I agree with previous posters that a foot on the ground would transfer force and negate calculations predicated on colliding bodies being unsupported. The angle of incidence with the ground would be critical. There's also the problem that the two players aren't shaped like blocks or spheres and won't be hitting one another center to center, so they are going to rotate around one another and the transfer of energy wouldn't be 100%. A human form will also buckle and change shape at impact, unlike a billiard ball or ideal object, so you've got moments of torque and a shifting center being introduced by the change in shape of the two players bodies in addition to linear vectors. And an unlucky player's body would buckle at a point where the force of impact is sufficient to overcome the integrity of a joint.
In all, an increase in velocity will do more to increase the force of impact than an increase in mass. When I was a kid, maybe 70 or 80lbs, I knocked a big fat dude a long way when I skied into him.