From a Craig Boddington book:

(a) Shooting positions: Standing.
My colleague and good friend John Wootters and I were hunting the other day and talking about this book. As usual, John had an astute observation: “One of the greatest boons to wildlife conservation would be to convince the American public that if an attempt is made to shoot a rifle standing up off the shoulder, with no rest, the rifle will simply not fire.”

Perhaps that is a bit extreme; once in a blue moon there’s a reason to take a shot at game from the standing position. But there’s no easy way to learn to shoot standing up. And, there is no right or wrong way to do it. …

(b) Shooting running Game:
Earlier in this book, I mentioned my good friend John Wootter’s astute comment about shooting at game from the offhand position. He followed that up by saying that the second best thing we could do for America’s game conservation efforts would be to convince hunters that their rifles would not fire unless their intended quarry was standing perfectly still.

Shooting at moving game is indeed difficult, and shooting at running game with any degree of consistency is beyond just difficult. Taking ill-considered shots at moving animals is undoubtedly a principal cause of wounded and lost animals.

From Shots at Big Game, How to shoot a rifle accurately under hunting conditions by Craig Boddington, (a) chapter 10, Shooting positions. (b) chapter 19, Shooting running game. Copyright 1989, ISBN 0-8117-1703-8