Yes, all of the players who missed practice on Sunday are defensive backs. The secondary has been pretty banged up throughout training camp, and that was once again the case on Sunday. Delmas and Greenwood missed practice after missing Friday's game against the New York Jets, whereas Weaver and Wendling were out for the first time in training camp.
Considering another day off for Delmas isn't a huge surprise, Greenwood's injury might be the most frustrating one at this point. He missed all of training camp last year, and he's barely practiced this year. The good news is that he did some running on Sunday, according to Tim Twentyman, but he needs to get back on the field soon if he wants to have any shot of making the 53-man roster.
The Lions will continue training camp with another practice on Monday morning.