Wouldn't you also need to compare this parallel to each respective minutes True Shooting % to give a blanket statement like that some actual credibility?
Maybe guys are just hitting a higher percentage of their shots, by coincidence, during the times Bradley is on the court. Not necessarily who he's guarding, but other players on the opposing team.
Wouldn't you have to run each opposing teams/players stats to see if there was a dip or spike in FG% when Bradley is on the court. Plus you also have to factor Free Throws, which is why true shooting percentage came to mind. Maybe teams are getting to the free throw line more often when he is in the game.....and by more often, I mean by circumstance, not a dip in Celtics team-defensive performance.
When it comes to measuring D, we have raw, factual stats like BPG, SPG, DEF REB, but the rest is kind of based on "eye test", as mentioned before. I refuse to think that Avery Bradley is solely responsible for dips in overall team defense, when he happens to be on the court.