Source: pp 137-138, A Concise Introduction to Logic (12 Ed, 2014) by Patrick J. Hurley
The red herring fallacy can be confused with the straw man fallacy because both have the effect of drawing the reader/listener off the track. This confusion can usually be avoided by remembering the unique ways in which they accomplish this purpose.
In the straw man, the arguer begins by distorting an opponent’s argument and concludes by knocking down the distorted argument.
In the red herring, the arguer ignores the opponent’s argument (if there is one) and subtly changes the subject.
Thus, to distinguish the two fallacies, one should attempt to determine whether the arguer has knocked down a distorted argument or simply changed the subject. Also keep in mind that straw man always involves two arguers, at least implicitly, whereas a red herring often does not.
I do not comprehend the distinction in the bolded (subordinate) clause. To me, the bolded seems only to use different words to describe the same error; ie: how can you distort an argument without changing the subject, and vice versa? What have I neglected?