http://www.nhl.com/nhl/en/v3/ext/CBA...A_2013_CBA.pdf
Since it was a breach of the Player conditions within the standard players contract, I had a look (Exhibit 1, starting on page 310). There's a few options for the Kings and since they used the term "material" breach, I suspect they have a lot more on Richards than him just signing up for slo-pitch team without written consent. It will be very interesting to see what comes out, but the Kings would not have played this card without a tremendous amount of confidence in their case.