Due to the loss of Crowder, and Bradley, I'm also worried about defense.
I don't feel Horford got any worse of a defender from last year to this year.
Hayward is taller and longer than Crowder, but not as physical or able to guard multiple positions.
The loss of Bradley hurts, Smart can take his place but he has to start to do it.
Brown will do nothing but improve as a defender, he certainly has the tools. Nice size, very athletic, bright, aggressive. He's already pretty good, I'm hoping he will get even better.
Amir was steady, and took on the assignments Horford didn't want. Fingers crossed that Morris steps up. I don't know much about him defensively, but he did defend small forwards while playing in Detroit, so he may be versatile.
Say what you want about Irving, but he shouldn't need help every defensive play, allowing the team to not have to switch continually, and play more of a a straight up D when needed.
Yeah, I'm worried too, but time playing together will help.