I recently asked the following question: https://sports.stackexchange.com/questions/5602/how-many-injuries-would-be-prevented-by-banning-slide-tackles
In order to narrow down the question, I provided an initial background into the question, broke it down into two smaller sub-questions, and suggested a conclusion that could be drawn from from the answers to the sub-questions and subsequently used to answer the question as a whole.
The two sub-questions asked for clearly-defined, statistical, evidence-based answers, in order to prevent close votes for being "primarily opinion-based". Surprisingly, even though the question had a clearly-defined, narrow scope, it was closed as being "too broad".
How is the question too broad, and if it is not too broad, is the closing of the question simply a reflection of the downvoters'/closers' inability and/or lack of desire to provide an answer?