Sports writing suffers from a lack of attribution. A 'league' source could be virtually anybody. It could be sue down in accounting. It could be another reporter. It could be someone that they have a friendly relationship with and the question was phrased, "how do you feel about Reid to Arizona?"
Source attribution should be as specific as possible. If your source doesn't want to be named, then you ask, "Can I call you someone from the front office involved in the coaching search for Cardinals has said.." and you go down the line. The further down the line you get, the more you should look for an additional source(s).
We're also part of the problem with the way we hang on every ridiculous rumor and go rushing to whatever site has the newest, zaniest information.