Every match model leans on the assumption that a team's recent past describes its present. A managerial change breaks that assumption on a single day, and the models take weeks to recover.
The model's memory becomes misleading
Strength estimates are built from previous matches, weighted so that recent games count for more. After a change of coach, those recent games were played by a differently instructed team.
The squad is largely the same, which is why the estimate is not simply wrong. Personnel carries over while structure, pressing height and selection policy may not.
So the model holds a blend of two teams and cannot tell which parts still apply. The uncertainty is real but usually goes unreported in the published number.
The new-manager bounce is mostly regression
Clubs sack coaches after bad runs, and bad runs contain a share of misfortune alongside genuine decline. Some of that misfortune was always going to reverse.
Results therefore improve after a change more often than not, whoever arrives. The improvement is partly the appointment and partly the timing, and the two are hard to separate.
Caretaker spells make the point neatly. They frequently produce the same short-lived lift without any coherent change in method behind it.
What changes quickly and what does not
Selection changes immediately, and a coach who prefers different profiles can alter a starting eleven within days. Set-piece routines are often reworked almost as fast.
Pressing structure and build-up patterns take much longer, because they depend on habits shared across the squad under pressure. Training time in a congested season is scarce.
The result is a team that looks different in selection long before it looks different in play. Early matches under a new coach are unreliable evidence for either verdict.
Why the fixture list distorts the verdict
A new appointment rarely lands in a neutral part of the calendar. The first few matches may be unusually kind or unusually severe, and the record reflects that.
Judging the change on those results without adjusting for opponent quality produces confident conclusions from almost no information.
The adjustment is straightforward in principle and usually skipped in practice. It is the single most useful correction available in the first two months.
How to read the first weeks
Underlying chance creation settles faster than results and gives an earlier read on whether anything has genuinely shifted in how the team plays.
Watch the shape of matches rather than the points won. Where the team wins the ball, how quickly it moves it forward and who is being trusted are all visible immediately.
Points earned in that window are the least informative thing available. They are also the only thing most previews will quote back at you.