And what if your other hand is otherwise occupied?
Oopps, here is a much better view and explanation and circumstance that you speak of. This would be the case of an FTF, incapacitated arm, holding a defensive position while racking, one handed reload and rack, or all of the above in this guys case. all very useful skills because nothing goes the way we imagine it. the way its done is using the rear sight to grab on a belt or some other study enough object.
As boy scouts say "be prepared" and "pack it in and pack it out"
but i digress...