One of the long time complaints we've had about the Eagles defense, and this stretches back to the Jim Johnson era, was that they never played matchups with corners. A guy would play a side of the field and he would cover whoever lined up over there. So essentially, the offense got to choose the matchups.
This is generally not how most teams work. They'll often send their top corner wherever the opposition's top WR goes. Jim Johnson never did this, Sean McDermott never did this... but Juan Castillo did a bit last year and seems to have fully embraced it this season. Ridding his defense of the talented, yet completely inflexible Asante Samuel probably helped that a bit.
The Eagles are now playing matchups. Last week, we saw Dominique Rodgers-Cromartie shadowing the speedy Torrey Smith. Nnamdi Asomugha would face Boldin sometimes, but also get moved in on TEs in certain situations as well. Brandon Boykin would always play the slot and its actually interesting that Nnamdi would not follow Boldin inside if he lined up there. The Eagles were confident that Boykin could handle him and he did.
"It's really the matchups," said Juan Castillo when asked what determines which CBs play where? "What can this guy do well? What can your guy do? Can he take him out? That's why we talked last week in the way we felt about the matchups and where we put Nnam and where we put [CB] Dominique [Rodgers-Cromartie]."
It seems so simple and almost silly to heap extra praise on Juan for doing it, but given that he's been able to make a change from what he's been "taught" by the Eagles for the past decade is really something he deserves credit for.