What does "loading toward the ball of the foot" mean?

“Loading toward the ball of the foot” means you press into the ground under the front of the lead foot. It does not mean you jump. That press works like a brake on the sideways move: you push down so the ground can push you back, and then you can push up. A lot of players think this is a jumping action. Watch the heels instead: the harder someone actually pushes into the ground, the more the heels come off. Vertical force comes from that press, not from hopping.