Summary: We augment standard branching Brownian motion by adding a competitive interaction between nearby particles. Informally, when particles are in competition, the local resources are insufficient to cover the energetic cost of motion, so the particles’ masses decay. In standard BBM, we may define the front displacement at time \(t\) as the greatest distance of a particle from the origin. For the model with masses, it makes sense to instead define the front displacement as the distance at which the local mass density drops from \(\Theta(1)\) to \(o(1)\). We show that one can find arbitrarily large times \(t\) for which this occurs at a distance \(\Theta(t^{1/3})\) behind the front displacement for standard BBM.