Secretory phospholipase A₂ (sPLA₂) is a class of interfacially active enzymes that selectively hydrolyze lipid molecules organized at interfaces like membranes. We present a simple theoretical model that relates the sPLA₂ action to the protrusions of the lipid molecules. The model explains (1) the observed enhancement of enzymatic activity by lipids with flexible, neutral, water-soluble polymers linked to their head groups and (2) the lag-burst kinetics of sPLA₂. It yields qualitative predictions of the effect of the initial composition of the membrane, the molecular weight of the polymer, and the composition of the hydrolysis products.