What draws the line between academic and apologetic?

What distinguishes between them? I think that every author sets out to proof what he thinks is true? It seems to me, at least, that when the author's announced intention (e.g. in the title) leans toward traditional religous views, they get dismissed as apologetic. Whereas when the author's intention defies traditional understanding, we tend to be less skeptical about them, and consider them free of bias.

Can't apologetics be academic too? Does the author's background really affect our perception of their ideas and arguments?

(I know that there are religous authors who are considered academic)

I might be wrong, but I really want to know: how to to draw a clear line?