An atlatl or spearthrower is perhaps humanity's oldest technology for accelerating projectiles. The dynamics prior to launch of the dart projectile have been much discussed in the literature. In this article we present a simple new model of launch dynamics and show that dart flex is not an important factor in determining launch speed, but it increases accuracy. The atlatl is a lever but only indirectly; the significant parameters for increasing launch speed are applied energy, and angular difference between force direction and dart direction. This study exhibits some instructive elements of Newtonian mechanics.