Class A Output stage Negative Swing
Q2 is acting as a constant current sink. In 'negative mode', part of that current comes from ground via the load, and the rest comes from +Vcc through Q1. Even when Vi is negative, Q1 will still have a positive Base-Emitter voltage because Q2 is pulling the output voltage down. 

As the output voltage goes more negative, more current comes from the load and less from Q1, either until the load takes all the current (at VL = -I*RL) or until Q2 saturates and cannot pull any lower (at slightly above -Vcc).