When Molly Weasley and Bellatrix are dueling during The Battle of Hogwarts, why didn't Arthur Weasley help?
Forgive me, as I don't know where he is during that duel in the books, I can only remember the film where they place him right behind her.
If he was in the vicinity and saw/heard, regardless of whether she could handle herself, surely his natural instinct is to join in and help defend her?