Every year there are players who don’t exactly hit the ground running when the regular season arrives. Whether it’s the first-round pick of the team or a free agent acquisition, sometimes players take a second or two to get acclimated to their new surroundings, system, etc.
It’s usually the case that the starting lineup to begin Week One is not going to be the same as it is in Week 18. Heck, sometimes it’s wildly different after just the first few games, and that usually stems from some seriously bad injury luck. At other times, those the coaches thought to be starter-quality players will underwhelm and force their hand to try either a younger or less experienced player in hopes they are able to make it click.