Why Hasselblad so hard to focus?

Fast moving kids are challenging to photograph with a hasselblad, BTDT. Fast film helps, either to get a fast shutter speed, or lots of depth of field at a reasonable speed.
Pre-focusing at a spot where they will be may help, though that works better if “where” is predictable. A prism finder is almost essential. At least you don’t need to worry about landscape vs portrait orientation.

C lenses are tough due to the design and metal focus rings. CF lenses are a good bit easier due to non-metallic, broader focus rings and better designs. CFi and CFe lenses are considerably easier to turn and yet still hold the precision that Hasselblad users want to rely on. I have one C lens, three CF lenses and four CFi/CFe lenses.

I do a fair amount of work in very cold temps so those later build lenses *really* come into play where as a C lens can literally be a pain without gloves on.