Too many respondents basing their thoughts on his contract. Underpaid does not equal underrated.
At best Crowder is a 4th, 5th, 6th guy on a championship team, yet it seems most wouldn't trade him for a considerably better player. He's a good player, but he's basically at his ceiling.
I get the attraction to his intangibles. But, IMO, he's not as valuable as Bradley, Thomas, or Horford, while his value over both Smart and Olynyk is highly debatable. JB should be able to defend at his level or better before the season is out.
Therefore, and considering that contract, I believe it makes him the most logical choice to be traded as the primary asset in any major deal Ainge may make. We'll see if I'm right. If he trades for a legit wing, Crowder will almost certainly be shipped.