The hard, almost straight plant of your front leg on a run-up throw. It brakes you abruptly and converts the energy of the approach into torso rotation.
It sounds backwards, but the fastest balls in handball come out of a braking action. The standing throw with a run-up is the quickest technique there is — take it as the benchmark and the standing throw without a run-up reaches 93 percent of it, the jump shot 92 and the pivot throw 85. The difference sits in the plant step: if the front leg blocks hard and almost straight, your linear momentum cannot continue forward and gets redirected into pelvic and trunk rotation. The arm is only the last link in that chain. The classic fault is a lead leg that gives way — every collapse is speed leaking into the floor, and it forces you to make up the rest with your arm. That is what your shoulder pays for. And braking force is load too: drill the plant step fresh, with the knee tracking over the foot.