Shooting moving subject (walking) at f/1.8 - poor hit rate in indoor light

Depth of field at f1.8 with an 85mm lens at 10ft from your subject is about 2.5 inches ahead and behind.  Even if you do nail it, what is that shot going to look like with only part of a face and body in focus?  To me, f1.8 and moving subjects are not compatible.

Ultimately, I suspect you might be happier trying a different shooting strategy - what about bouncing some flash?

Mark