An explanation is intended to explain why some phenomenon happens. In this case, there is evidence that the phenomenon occurred, but it is trumped up, biased or ad hoc evidence.
This is a fallacy because the supposed cause is unsupported by the evidence.
The reason why most bachelors are timid is that their mothers were domineering.
This attempts to explain why most bachelors are timid. However, it is shown that the author bases his generalization on two bachelors he once knew, both of whom were timid.
The reason why I get four or better on my evaluations is that my students love me.
This is a fallacy when evaluations which score four or less are discarded on the grounds that the students did not understand the question.
The reason why Alberta has the lowest tuition in Canada is that tuition hikes have lagged behind other provinces.
Lower tuitions in three other provinces - Quebec, Newfoundland and Nova Scotia - were dismissed as "special cases" [again this is an actual example]
Identify the phenomenon which is being explained. Show that the evidence advanced to support the existence of the phenomenon was manipulated in some way.