Ground Marshal reported a technician drove a lift platform truck into the safety zone and under the aircraft wing during pushback. Ground Marshal gave a stop signal with wands but pushback continued.

Narrative

During pushback on flight to ORD; I was wing walking the pilot's side of the aircraft. I was in position with a line of sight to the pushback operator; and upon receiving the signal that the aircraft was ready to push and seeing the beacon light illuminate; I gave the safe to move signal. Shortly thereafter; the pushback driver began to push the aircraft. At this point in time; an aircraft maintenance worker entered his vehicle (a lift platform truck) just outside the OSZ (Outer Safety Zone); also on the pilot's side; and looked in my direction. I believe that he saw me walking the aircraft out; but I can't be sure. Then; although the beacon light was flashing and the aircraft was moving; the maintenance worker drove directly into the OSZ and passed beneath the wing of the aircraft before exiting the gate area and driving off. I gave the stop signal with my wands as soon as I saw him enter the OSZ and maintained it until he was clear of the OSZ; but the push continued anyway. After this incident; the push continued uneventfully and the aircraft departed.