AUTO RUN activates SPRINT / RUN while the MOVEMENT ANALOG STICK is FULLY moved FORWARD to the EDGE. This allows for walking or jogging to avoid giving away your position.
To keep Auto Run from cancelling your reload, there is a delay after PRESSING RELOAD before it can activate SPRINT / RUN again.
Whenever you finish grappling or rappelling, TAP or to resume Auto Run.
or 
to resume Auto Run.