The Vikings backup quarterback controversy brings into focus the importance of preseason game performance, and game performance in general, as part of the overall player evaluation in determining depth charts and roster spots.
Conventional wisdom is that while practice matters and is an important part of a player’s evaluation, performance on game day is paramount. At the end of the day, if the team loses in part because of poor performance by one or more players, there is little consolation in explaining, “yes, but he’s good in practice....”
Most coaches would agree, however, that players who practice well tend to play well, and vice versa, although there are exceptions.