In 1 Samuel 20:30, Saul makes a very confusing accusation against his son Jonathan in the wake of discovering that David had escaped his hand by Jonathan's aid (the whole feast followed by shooting arrows into a field scenario). It is an accusation whose language Saul takes directly from Leviticus 18:7, and it refers to having sexual relations with ones mother, Oedipus style.
This is all clear enough. The confusion is why the accusation is made, and why it is made here, and I came across the (possible) answer purely by accident. I had gotten off work on Saturday morning, and, purely on a whim, decided to have breakfast before going home and going to bed. So, I went to the Breakfast Club and was invited into a Bible study taking place, which Peter Leithart was leading at the time. Anyway, here is the theoretical explanation given.
By explicitly contradicting his father's wishes, Jonathan is acting as if he had no paternal obligations to Saul, which could in turn give rise to the theory that Saul was not his father. Saul's accusation is far-fetched, but Leithart's explanation fits, and, as I know of no other that does, I am adopting that as my working theory of the verse until I find something else that fits better (this is me hinting to all three of you--readership is climbing--to suggest alternate theories in the comments section).