A form of overfitting is fairly common in sports, namely to identify patterns to explain past results by factors that have no or at best vague power to predict future results. A common feature of these "patterns" is that they are often based on very few cases so that pure chance is probably the most plausible explanation for the pattern.

Examples include things like (the "quotes" are made up by me, but often look similar)

Team A has won all X games since the coach has starting wearing his magical red jacket.

Similar:

We shall not be shaving ourselves during the playoffs, because that has helped us win the past X games.

Less superstitious, but a form of overfitting as well:

Borussia Dortmund has never lost a Champions League home game to a Spanish opponent when they have lost the previous Bundesliga away game by more than two goals, having scored at least once themselves.

Similar:

Roger Federer has won all his Davis Cup appearances to European opponents when he had at least reached the semi-finals in that year's Australian Open.

The first two are fairly obvious nonsense (at least to me). The last two examples may perfectly well hold true in sample (i.e., in the past), but I would be most happy to bet against an opponent who would let this "information" substantially affect his odds for Dortmund beating Madrid if they lost 4:1 at Schalke on the previous Saturday or Federer beating Djokovic, even if he won the Australian Open that year.