Marth Crouch Canceling Question

[StealthyPanda122]

So a lot of theory about marth that I've read has mentioned Cc'ing stuff like fox and cfalc's nairs or jabs or cc sheik stuff. The question I have is what do I do to counterattack? especially in the event that they cross me up. I guess dtilt/grab would be fine if they land right in front of me but if i cc a crossup'd nair from cfalc or fox it seems like i'll just eat it and they'll be behind me now.

If it turns out that cc is not the appropriate response to crossup's nairs, then what is?

 

[Sycorax]

You can turn around grab.

 

[RazeriaN]

I usually just grab, but if i notice my opponent trying to roll behind me I'll just down smash