The purpose of this study was to explore the usefulness of a markerless open-source human pose estimation algorithm, for estimating centre of mass (CoM) velocity in the javelin throw at three discrete time instances: the last right leg touchdown (RLTD), brace leg touchdown (BLTD) and release. Forty throws from four right-handed javelin throwers were simultaneously captured with two high-speed video cameras and a 16-camera marker-based Vicon motion capture system. For horizontal resultant velocity (Velhor), the method demonstrated excellent validity at RLTD, whereas at BLTD and release errors were notable. Based on these findings, CoM Velhor can be estimated using the proposed method with promising accuracy at RLTD. At BLTD and release, using a CoM segment model with arms in more optimized measurement conditions might further improve the accuracy