Particle distributions of bursty bulk flow (BBF) events in the central plasma sheet regions show that the high earthward mean velocity comes from a combination of energetic ion flux increases (>few keV) in the earthward direction and decreases of similar energy fluxes in the tailward direction. The energetic ion increases are observed to ~few MeV during intense events, indicating the responsible mechanisms efficiently accelerate particles. The BBF events are intimately tied to the dynamics of tail current sheet reconfiguration and for the two events discussed here, they occurred 45 minutes and 5 minutes after the expansion onsets. The perception offered by our analysis differs from the earlier studies which described BBF events using MHD approach. ¿ 2000 American Geophysical Union