This is from the locked thread, but seems relevant here...
I think its the injury. Though he is starting to become the Jacoby Ellsbury of the Celtics.
This is my problem with Bradley longterm (and the reason I would strongly consider trading him if anyone values him high enough).
When he is healthy, and playing 100%, he is a gamechanger. However, if he is nicked up a bit, he drops from a gamechanger to just a really good defensive role player, and then there are the times when he can't even get on the floor.
He is just so small to play as physically as he does, and he isn't skilled enough in the other parts of the game to not be that physical, without being much less effective overall.
So what it comes down to is that he likely has to be a part time player. The chances of him staying healthy, and being able to give the full effort that we need from him are so slim.
Unfortunately, I am not sure anyone else is high enough on him to give up the value thats needed to make a trade worthwhile for the C's.