TNA decided recently that they would not renew Booker T's contract when it expires in november for many reasons, one being his refusal to put over Matt Morgan During a TV Taping recently. Booker is said to have been very negative towards and basically acting like an ass****.
No one seems to know why booker started to act this way, but many say it is because he was not happy with the company direction, either way once he left TNA he did not have a bad word to say (even saying he wishes TNA well).
Now that Hulk Hogan is in TNA there are strong rumors that Booker has interest in re-signing with TNA (but TNA do not want to resign him), However if Hogan wants Booker to rejoin then it will likely happen. Booker likely feels that with Hogan onboard TNA will be run correctly.
