Since last season, the Cs are 25-9 with Bradley starting, and 33-35 when he doesn't start. Percentage-wise, the Cs are a 60 win team with AB as a starter, and a 40 win, late lotto-team when he doesn't start.
There isn't a huge sample size here, but it's clear that the Cs are a lot different team with Bradley. The defensive difference has been noted many times, but there is a couple of other differences when he's in the mix. In Bradley's six games this season, the Cs have played like one of the best defensive teams in the league.
First of all, the team becomes a lot more consistently competitive. When you have a defender who plays wallpaper-y on the ball defense, the rest of the team naturally perks up defensively. Offenses now have less times in their half court sets, which results in less ball swings, which means the defenders have to move and recover less. Offenses make more mistakes and throw up more bad shots late in the shot clock.
This pressure and heightened team defense, leads to run outs, from turnovers, and long rebounds of late shot clock shots.
AB also brings a ton of toughness to the team. It's not typical NBA toughness, usually done by big men throwing their bodies around. It's a doggedness. The guy keeps coming at you, with consistently high effort, and crowds your space the entire game. AB is often compared to Tony Allen, but Allen's defense his first few years was never applied as consistently as Bradley. One other of AB's more positive attribute is that he's unflappable. His stone faced demeanor must be frustrating to NBA scorers are used to doing what they want on the floor.
One interesting thing about the Cs recent five game winning streak with Bradley is how poor he's been on offense. For a guy who showed great shooting accuracy last season (50/40/79% overall, a ridiculous 52/50/84% post-all star break), this year Bradley can't throw the ball into the harbor from the pier, shooting a gristly 35/21%. These numbers should jump as Bradley shakes off the rust and plays more.
The great thing about Bradley is that he's all upside, even defensively, where the more games he plays and more accolades he garners, the more NBA refs will give him the latitude to play his game without getting whistled for ticky tack fouls.
Offensively, I think he's got a chance to me a more than capable scorer. How many guards, in their first year in an NBA rotation, at age 21, shoot 51/56% on the road? A young guy, in new arenas with fans cheering against you, with that kind of shooting success tells me that Bradley is a mentally strong player.
The only thing that could hold Bradley back is the injury bug. Maybe he can stay healthy this summer, and actually fully participate in a training camp.
The Celtics have two very young players who are unique in the league, in Bradley, who recently turned 22, and Jared Sullinger, who still can't go to Sully's and (legally) drink a beer for another two months. Acquiring this quality of player at picks 19 and 21 is what will allow the Cs to stay competitive for a long time.
There will be a lot of temptation to move them both to add someone who is perceived to have a lot more upside, like DeMarcus Cousins. If I were GM, I'd have to make that trade, based on Cousins' upside as a top 3 center (and Bradley's injury history). Before I did pull the trigger, I'd evaluate how valuable Bradley's effect on this team's success is compared to whatever a big's hypothetical effect would be, and whether at least some of that effect can be added through a lesser move.