I'm not an expert in all contractual things but if the Rams own AD for the next few years, why should they give him a huge chunk of change now? AD is contractually obligated to play next year for what he signed for as a rookie. Then, if I understand things right, the Rams could "tag" him for the next two year at some significantly higher rate, but probably not as high as free agent rate.

If they own the rights to AD for the next 3 years, why re-sign him now? Why guarantee him cap money when he's only an injury away from being broken?
Perhaps I am missing something but why not wait until he's due?