A Stinging Insult

ASK FANTASY FLIGHT 

Q: If I declare an Arcona Rumor Monger as a lone attacker and then play A Stinging Insult, does this compel my opponent to declare a 2nd defender?

A: No. Your opponent MUST declare the target of A Stinging Insult as a defender, but if he chooses not to declare a 2nd defender, the Arcona Rumor Monger will cause the declaration to fail. The "if able" line on A Stinging Insult allows this to happen and the opponent will end up not defending this engagement.